I happened upon MBTI just a few years ago, and from tests and reading up on the 16 types, I have always believed I was an INTJ.
However, recently, I have found that there is a slight possibility that I may be an INTP, or possibly even an ISTP. I just know for certain that I am an IxTx.

I'm not quite sure why I'm suddenly doubting my type, but I am, so help is welcome...?
Below are my answers to a personality type questionnaire.

1. Is there anything that may affect the way you answer the questions? For example, a stressful time, mental illness, medications, special life circumstances? Other useful information includes sex, age, and current state of mind.
The only things in the way are the fact that I am currently undergoing a week of tests and the extremely high possibility that I may suffer from depression. I am female (and I identify as one).

2. What type(s) do you usually score as on tests?
I often score INTJ on regular tests, but I've found that on cognitive functions tests, I usually score either INTP or ISTP.

3. You are on the clock to fix something, a friend of yours sits beside you and gives a lot of interesting ideas, none of them actually help or are related to your situation, but they are still something you find interesting. What is your reaction? What do you say? What do you do? What's your train of thought?
I'd most likely just ignore them, and be obvious in the fact that I do not appreciate the distraction. Whether or not I choose to show it or tell them directly depends mostly on whether or not I am close to him/her. If I am not, I'd most likely just inform them directly that despite the fact that I find the ideas interesting, they are not helpful, and thus the person is not being helpful and I'd much prefer if they'd leave me alone. If I am close to the person, I might be more patient.

4a. What are some of your most important values?
Ambition, curiosity, trustworthiness, loyalty, intelligence, and common sense.
4b. Can they change? What would be the reason if they changed?
They might. So far, they have not. Or at least, if they have, only slightly since I have not noticed any/much change. The only reason I can provide for them changing is the change of my lifestyle.

5. You are in a car with some other people, the people in the car are talking. Someone makes a claim that you see as immoral/rude/cruel. What is your inward reaction? What do you think? What do you say?
I'll definitely notice it, and I might just think, Wow, that's very rude/immoral of them. If it's extremely rude, I'd call them out on their statement. If I usually enjoy the person's company, I might ask them why they would say such a thing. The other option would be just to ignore the person. Opinions are opinions. I don't have to care if it's not harming me.

6. a) What activities energizes you the most? Why?
Activities that provoke my curiosity. If I'm curious about the subject, I'm more likely to want to participate.
(ie. that single visit I made to a wonderful library quite far from home energized me. The amount of books there along with the amount of knowledge I could gain energized me.)
6. b) What activities drains you the most? Why?
Activities where I am forced to socialize with people I dislike or activities that require me to put in a certain amount of energy whereas if I were to do it on my own, I'd most likely execute the task without wasting any.

7. Do you believe you are introverted or extraverted? Why do you believe that? (Please be as detailed as possible)
I am highly introverted. I consider only two people in my life as friends (though there are probably a handful of people who would consider me as their friend). I am not quite shy, but I keep to myself for the most part, and weeks of not socializing with a great number of people would not kill me. Socialization is not vital for me.
I can also get extremely stressed out if I spend too many hours socializing.

8. Please describe yourself, what do you see as your greatest strengths and what do you see as your greatest weaknesses?
My greatest strengths would be my ability to adapt extremely easily - usually in terms of personality - as well as my ability to learn new things with ease, and my open-mindedness.
My weaknesses are most likely my pride and my habit of over-analyzing people and situations. My perfectionism, my disinterest in befriending others, and my lack of empathy (though there are sudden moments when I can empathize with people, or more often fictional characters) could be considered weaknesses.

9. Please describe yourself when you are feeling stressed. How do you act and why? Real life experiences are welcome.
Stress can either lead me to depression or simply energize me to continue with whatever I'm doing. I've had a nervous breakdown after being assigned projects all due within a relatively close time period, and I was doing them all last minute because I had been too busy with other assignments. I may act more agitated when forced to socialize, and may be looking for every loophole to avoid interacting with others if I'm stressed. I need to get something done and interaction is just an unnecessary distraction. At the same time, I may even be in need of a distraction, finding any opportunity to procrastinate. My response to stress varies.

10. What is your "soft spot" (the area that makes you upset if people mess with)?
Not quite certain as to what this question pertains to, but I do get irritated if people take advantage of my kindness or my care. I'm not exactly the kindest person in the world, so if I trust you enough, it means a lot. Going back on your word pisses me off, even though I might not express it.

11. What are most of the ideas/thoughts you get generally centered around (try to expand your answers as much as possible)?
Again a strange question, but I'll answer it as best as possible...? I tend to introspect about life and death, along with human nature.

12. What's your opinion of getting frequent feedback on what you do? (Someone pointing out what is good, what is bad, what and how to improve) Is there a limit to how often you want feedback? If so, what is the limit?
I don't want feedback if I don't ask for it. However, I do like a fair amount of feedback on work I do from people I respect. My English professor, who is quite interested in philosophy, is someone I respect very much. I don't mind hearing about my weaknesses, and hearing about it is sometimes important for me to improve. The positives aren't necessary in feedback, but praise is...nice.

13. Anything beyond what has been discussed that you would like to add?
- Perhaps I should've said this in my first answer, but there's also a high possibility that I suffer from antisocial personality disorder.
- I have a tendency to only form friendships or at least stay on people's good sides only in case I need to, uh, use them.
- I follow rules, but they're not among my top priorities. I'll break them if they're illogical.
- I'm pretty sarcastic and snarky. I was not aware of the former until recently. Apparently my compliments sound quite fake.
- I try to be organized, but there are occasions where I am not successful.
- Again, I think it's important to note that I am very adaptable. ie. I'm currently in a musical only because it seems like an interesting experience and because I'm a decent singer. Still, I have boundaries in terms of how "out there" I can be, so if I reach one, I usually just use other actors' energy and run off theirs to avoid feeling strange about whatever I may be doing.

So, any ideas?

P.S. If it matters at all, I'm a type 5 enneagram (with a very slight preference of wing four over wing six).