Ok, I just checked out your age - 20 - and that's still kinda young in terms of personality development (in my opinion). Now I'm gonna make myself sound all old and stuff, but I was pretty clueless as a teenager about my personality (in hindsight, I'd call my teenage self half-formed/to-be-determined), and given my lack of friends, social ineptitude and inability to click with really anyone on a deep level, fear/dislike of many of my peers, my interest in math and science and disinterest in many of the the more stereotypical 'F' pursuits/inclinations, I would have tested as T, and really related to the T descriptions. I'm reasonably certain in my teens I would not have tested or identified with INFJ, and even in my early 20's I did not test as such or see how I could possibly be an NF.
All of this is to say...growing up is the process of learning more about yourself and honing in on who you are...and a lot of that happens in ones 20's. Or maybe I was just stunted and I was a really late bloomer. (by the way, I'm not trying to be patronizing or anything, although it probably comes across that way)
So maybe in your late teens you identified with INTP. Maybe in another few years you'll have come to new understandings of yourself and you'll realize that's not your 'best fit', and really you're more INTJ. Or, maybe INTP will just take root even deeper and you'll continue identifying with it.