Gi bleeding after sex?

Not sure. Certainly it could be hemorrhoids from straining during intercourse. I am making an assumption that we are not talking about anal intercourse. I strongly recommend avoiding anal intercourse. It is an exit not an entrance!
Not usual. It is not usual to have GI bleeding after sex unless there is some trauma involved, such as if there is anal sex; it is likely to be a separate event; perhaps a hemorrhoid happens to be acting up;.
Not enough info. Should see a doc to figure out what is bleeding and how to prevent this from recurring.