I Am On The Pill Since I Can Remember And

I am on the pill since I can remember and I know my cycle like the back of my hand and my monthly bill came a week and a half early this morning. I have very very bright red bleeding with severe cramping and lower back pain with nausea. I never have back aches or nausea and my cramping is never this bad. Could it just be an early period or am I having a miscarriage?