This was me at age 18. I wanted to go away to college, stretch and find new friends. Then I actually got there, and didn't really know how to do it. As a result, I got more reclusive, gained about 40 pounds, and wound up leaving that school after toughing it out for 3 semesters. I eventually went to a local college and got my degree.
In retrospect, and not knowing my "condition", I simply tried too hard, and had no idea how to be extroverted - it just sounded like the thing to do. Knowing what I know now, if I had it to do all over, I would have not thrust myself into that situation. I've since found my niche and figured out how to slowly open up, but when thrust into unfamiliar situations without warning I tend to calm up still.