The other day I was having sex for the first time in a few months. I started bleeding, so we had to stop. The bleeding continued for the next day and then stopped. Today, I started bleeding again after and it is heavier than before. It seems to only begin during times of sexual arousal. I've been on the birth control shot for about four month, but I've never bled or experienced any cramping. I just got a shot this month, but I've had sex while using the shot before and this has never happened. What could be wrong with me? I don't know whether something's wrong or its just the shot's side effects.