Sounds like a possible early miscarriage to me. Sometimes if the blastula (embryo) doesn't implant well enough or the hormones don't shift soon enough or if there is something structurally or chemically wrong, the body will flush everything out and start over. I don't think there is anything wrong with you and I doubt that you are pregnant, but, to be sure, you can purchase an early home pregnancy test to see.

I'm sorry to be the bearer of bad tidings - I know how disappointing it can be to start bleeding when your hopes are high - just know that the body usually has a good reason for what it is doing and it really will be better in the long run to start over and try again.