You should get yourself checked because irregular periods raise the chance of uterine cancer a lot.
This -- should have a menses at least 3-4 times a year the last I talked to a doc about it. Provera I've requested before when not on BCP.
I'm in the same boat, though I do have PCOS and at my weight, the symptoms are more annoying -- hairy chin, acne, etc. When I was younger and slimmer, the only real problem was lack of menses though. So perhaps you have a light case? Or some other thing messing with your hormones?