I'm gay I had "sex" last week and from that day I'v been pooping with blood is it Serious?

Yes of course its serious. Blood vessels may have erupted in your anus, may have caused abrasions, contusions from no lubrication. These could become infected with fecal matter and cause many problems. I know you don't want me to say this, but go see a doctor to determine if any long term damage has been done. Anal sex same as vaginal sex should be accompanied by condoms and lubrication.

Tick

Especially serious if it's still going on... hope you got help man.