I am 17 and a junior in high school. I started my period when I was a freshman. they were never regular. They ranged from 2 days long to 2 weeks long and would happen ever couple of months to maybe even twice a month. I started having sex so I got on birth control, then I stopped taking it about 8 months ago. Since then I haven't had a period. I started running about 6 months ago for my schools track team, we run about 6 miles a day. My periods were still irregular tho before I started running. I weigh 120 and have weighed that for years now. I'm just wondering what is going on, if you need any more details I'll be happy to give them!