Congratulations!! A similar thing happened to me last week!! I had AF and then a BFP 13 days later. Turns out I'm 6 weeks pregnant so i must have conceived last cycle and the bleeding was implantation bleeding or somthing (or possibly the loss of a twin). Anyway, that bleed was exactly like AF - nothing to make me suspect it wasn't at all.

Get to the Dr and get a BT and a dating scan to determine how many weeks you are. That sould give you a better idea of what is going on.