I got a fever of 103, and my cheek is swollen. My doctor prescribed penicillin, and hinted that it may be mumps. Is there a test to see if it is mumps?

Penicillin response. In recent epidemics we have been seeing cases of mumps even though the patient has been immunizedresponse to penicillin will tell you if its mumps or parotitis.
Vaccinated? If you have been vaccinated it should not be mumps. If you are not sure then it could be but penicillin will not be effective against it because mumps is caused by a virus. If the penicillin helps then you likely have an infected tooth and you may want to see the dentist to have that checked.
Mumps? Mumps is a viral disease and because of vaccinations we do not see this condition much these days but unvaccinated people and children can get mumps.It is caused by mumps virus and we do not use antibiotics to treat mumps.Usually it is diagnosed clinically by examination.If you are not sure of the diagnosis then atest on saliva or blood using the real time PCR technology.Serum amylase may be high.