I did have a pregnancy on the first ovulation after a miscarriage (but in my case, I miscarried again -- probably due to no supplementation with progesterone which I later found out was my problem). You should schedule an appointment and get an early ultrasound to see what is going on, how far along you really are. The earlier you get a dating ultrasound, the more accurate it is.
I know two people who were taking pill or emergency contraception early in pregnancy and both turned out just fine, so I wouldn't worry about that.
DS1 (6) , DS2 (3) , DD is here!