I started my cycle at 8 always regular. in 2012 ihad three cycles in may nov and dec dec lasted 12 days started again 2wks later. what could be wrong?

External influences: Despite what most think of as an automatic and simple system, there is a very complex interaction between several hormones, each of which can be impacted by different life stressors. Infection, trauma, external stress (emotional/social/etc.), diet change or inadequacy, among others, can all impact the reproductive cycle. If irregularity persists, you should see a gyn.