Abnormal periods..?!

I'll be 18 in a few months and I've had mine since I was in 7th grade, and it still hasn't evened out!. I get it as much as every month and a half, and up to 3 months can go between them!. I don't want to go on birth control because I'm scared I'll gain weight, and I don't want to have it every month!. I don't eat very healthy, but I'm still very small (105 lbs) so I think my diet has something to do with it!. Any advice!?Www@Answer-Health@Com

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