you're right that your type probably isn't changing that much. :]
people often test as what they wish they were and are often affected by their moods (if you're depressed, you might answer a question cynically for example).
i also test lots of different things... INFP, INFJ, ENFP, and ISFP - once even INTJ - depending on how i'm feeling that day, and how good the test was!
my personal guess (based off little info lol) is that you are a fairly socially-extraverted ISFP, and you pull in iNtuition to give you extra help when things are going poorly, but your natural preference is for Sensing. ISFPs are known to be the most "extraverted introverts", which may account for your feeling ExFP often.
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if you want to get deeper into being sure of your type and learning about the MBTI, the
Understanding the Eight Jungian Cognitive Processes / Eight Functions Attitudes site has descriptions of all the jungian functions, which are the 8 cognitive preferences that technically determine your type. they're combinations of the regular letters N, S, T, and F, plus "attitudes" - whether someone uses them to look at the external world (extraversion) or the internal world (introversion). the combination will give you a function like
extraverted Sensing (often abbreviated as Se), which means looking at the external world through the lens of Sensing.
an ESFP prefers primarily extraverted Sensing (Sensing applied to external objects/people/ideas) and secondarily introverted Feeling (Feeling applied to oneself and what lies inside objects/people/ideas); an ISFP prefers introverted/internal Feeling first and then extraverted/external Sensing; and an ENFP prefers extraverted/external iNtuition and then introverted/internal Feeling.