Nine days after unprotected sex I vomited?

Could be anything. It may be a coincidence. The vomiting may be related to a stomach illness, something you ate, a viral illness, or (what you are most likely concerned about) pregnancy. Get a pregnancy test done, to rule that out. If the vomiting continues or additional symptoms begin, then see your doctor. Unless you are trying to get pregnant, you need to start taking precautions against pregnancy.