Gaining weight also can throw you off. It's well-documented that heavier women frequently have weird menstrual cycles. (I speak as one of them.) I started at age 10(!) and was regular as clockwork for the first few years, but not since (32 years later). The pill helped, and then I spent 3 weeks in the hospital with a blood clot in my lung. That was the end of hormones for me, and it's been a mess ever since.

Nevertheless, those are only my experiences -- a gyno visit should be in order, for sure. My only tip is to find a female one! My first "girly doc" appt. was with a weird old man who cracked jokes the whole time, which was not only thoroughly inappropriate, but made it even more uncomfortable. (And it is a little uncomfortable, but really not too bad.)

Good luck.

CB