Light brown discharge during 6th week of pregnant only when wiping. having some slight cramps, heartbeat was heard on 6w 3d, what could cause the bleeding?

First tri bleed: It is pretty common to have some bleeding/spotting during the first trimester. It does not have to mean that anything is wrong. We see bleeding from small subchorionic hemorrhages all the time with successful pregnancies. Let your doctor know if this is a new symptom, and s/he may want to see you again sooner than your scheduled appointment.