Hmm I am more tender round my CS scar but while I have had bleeding every pregnancy it hasnt been to do woth my CS's. My first pregnancy I lost then with DS I had bleeding before 12 weeks and I then had him via emerg CS, got preg with DD, had heavyish bleeding before 12 weeks with her(was a pocket of blood under the sac) and had her via elective CS, and this one, I had some bleeding at 4 weeks.
Sometimes bleeding is just random and unexplained, try and not worry and I would see about another scan to ease your mind