Freaked out

I need some advice. This might be a long one.

I guess I should start by saying I began puberty at 7, first period at 11. Im 21 now, and for the past 3 years my periods have gotten more and more irregular and more and more painful. From 11 to 18, every month on the dot. Perfect. Then a 31 day cycle, the new norm. Now I get a 15 day cycle here, then 30, then 42, then 35, then 15 again.

I'm not on birth control, I'm pretty healthy, though a bit thin and I smoke moderately. I've never been to an OBGYN because my family was weird about it and I haven't been independent for long.

I guess all I'm asking is: should I be as freaked out as I am? How do I make an OBGYN appt if this stuff is cause for concern? Any theories as to what it might be? Discuss.