Well it's altogether possible that your cycle went a little off and you had an early period. It's also possible that you had some tearing inside your vagina and you were bleeding from that - you might want to get into a doc so she can check you out and make sure there are no injuries! Please be careful during sex - it it hurts don't proceed - protect yourself

!! Also to avoid future painful sex or injuries make sure you are fully aroused (your vagina will open up bigger generally and you will be wet) or at the very least use lube. One of the things no one ever talks about is making sex not-painful for women, or what happens to women during sex (everybody and their momma knows men get hard, but no one knows women are supposed to get wet and open up).
What the blood actually is would be hard to say for certain over the internet, truth be told.
A bit about implantation bleeding: it doesn't always happen (in fact it's not the norm) and it would happen 2 weeks after ovulation, which means if you were going to have implantation bleeding, it would happen usually right about the same time your period would start. So the possibility of the blood you had being implantation bleeding seems to be slim.
Other than that, get yourself to a gyn and see what she has to say about the bleeding - just from what you said it sounds like injury blood, but I can't say for certain.