I had 2 really bad bleeds when pg with DS after dtd. Both times I rang the midwife and she made me come up to the hospital to get checked, and the first question she asked was 'What had we we been doing' Apparently it is really common. As long as it stops and doesn't get heavier, you just need to take it a little easier, but it should be fine. It also happened when I was pregnant with the twins. We stopped any action after that - poor DH