Hi I Am A Male And I Just Had Anal

Hi I am a male and I just had anal sex with another man for the first time in a long time (he penetrated me). There was no lubrication used, when I ejaculated there was a lot of blood in my semen. This has never happened to me before, I have not even passed blood in my urine before.
I do not know if I may be carrying any STI's, but as far as I know I don't. I was wondering why this might be and what the possible causes may be.