Bleeding From Nose In Winters, Irregular Periods, Random Dizziness. Pregnancy Ruled Out. Cause?

I am 15, and I hve had my period for a year and a half. I get very bloody noses I m the winters, but recently try have been way more frequent than usual. I haven t had my period in 3 months but usualy it is very regular. I eat very healthy and practice yoga 3 times a week and bike regularly. I thought the reason that I was missing my periods but today I got extremely dizzy in my yoga class. I also took dairy out of my diet and thought that could be a reason. There is no way I am pregnant, by the way. Please help, I m very curious.