Female problems, Please answer only if you are serious and are a mother. ?

I am 21 and have two kids, 3 and 1 years old. About two months ago i started to have really bad stomach cramps, heavy bleeding, and back pains while not on my regular period. I am on birth control and have been since i gave birth to my one year old. Also i am not pregnant. My question is.... what could be causing this? could i be having a early menopause or what? I have a doctors appointment coming soon and kinda also wanted some hints on what i should ask the doctor.