It’s not uncommon for people to get a small injury when they masturbate.  Being a little rough or having some lubricant find its way into your urethra (the pee hole) can cause irritation and pain.  As long as it gets better in a few days, I wouldn’t worry about it–sounds pretty normal.  If your penis has not touched anyone else, it can’t be HIV or a STD.  Just so you know, most STIs males get DON’T cause symptoms–you can have them and not know–which is why it becomes important to get tested regularly (usually yearly) once you choose to become sexually active.