My son is 5 months old and we don't know if hes theeting yet or not but he can't keep any of hiss formula down at all what's the problem?

Probably stomach bug. Teething has been wrongfully blamed for causing diarrhea, vomiting, rash, and fever (over 101 f). You may introduce small amount of pedialyte often for an hour or two. If kept well, you may reintroduce formula, small amount to start. If not, seek medical attention before he becomes really dehydrated.
Don't know. I cannot tell from your question exactly what is causing your son to spit up. If at any point your child is running a very high fever or you feel is not getting adequate nutrition you should see your pediatrician.