Try not to panic, do call your Dr, and explain what is happening. When I miscarried I started lightly on a Thursday evening and got heavier by morning and didn't have any cramping at all!!! Just try to take it easy, it may be nothing, but not to be graphic but when mine got heavier I started passing clots! Then I passed what I thought was the baby, We met the Dr at the ER and he did an ultrasound and there was no heartbeat, and I had blood drawn for HCG test and then had to go in to the office 2 more for followup blood work to make sure the #'s dropped low enough.
I wish you luck! How far along are you? Some people do have AF during pregnancy, have you ever been told that you have a tilted uterous cause I know that can cause bleeding during pregnancy like AF. Try not to worry it may be nothing, I will have you in my prayers, keep us posted.