You can google up the cognitive functions of the types, especially dominant and auxiliary ones, and then read over the descriptions and see what you can relate to the most:
INSPs - introverted feeling dominant, extraverted sensing auxiliary
INFPs - introverted feeing dominant, extraverted intuition auxiliary
INTPs - introverted thinking dominant, extraverted intuition auxiliary
Also visit forums of these MBTI types and read over the sticky threads. There are usually threads like "you know you are such-and-such type when" where people post characteristics that they thing are specific to their type. After reading through these threads you may find that you relate more to one but not others.