I started mine at 11, Now at almost 16, I might get it sooner than once a month, I might skip for 4 months. It might be light, It might make me extremely ill. I might have signs 2 weeks before, I might not have any signs at all. It might be a short cycle, It might be a long one. I might have a cycle where it worsens my mood swings, I might be mellow. I might have extremely odd cravings, I might not have any. Every part of it is random for me.
My doctor didn't have a reason for it (other than stress), So I suppose if you're not overly stressed, Underweight or pregnant, You should be okay. You should probably bring it up with your doctor next time you go for a check-up, Just in case, Though.