Bleeding after sex - need advice!

Chulee
So last night my husband and I had sex - as you do when you're trying for a baby... 
However after getting the deed done I went to the toilet and noticed that I was bleeding (only 2-3 drops), however I then noticed what looked like a blood clot in the toilet, it would have been the size of a five cent piece. I have had very minor cramps today but no bleeding at all! 
We have been trying for 10 months now and my ovulation day was 7 days ago. We are both clean people, have been tested for everything prior.
What does this mean and why do you think it's happened?