Unfortunately, an unbearable sore throat is a symptom of mono, and unless your doctor thought you had a superimposed infection to begin with, you should not have been prescribed an antibiotic in the first place.

What can be prescribed in a few circumstances is steroids (i think more specifically corticosteroids). Steroids act as a super anti-inflammatory and can help ease the pain and swelling of the sore throat. Other than that, symptom relief is the only thing to do. I know your pain though, I'm suffering from mono at the moment myself. The only thing that seems to give me some relief is gargling beef broth (ewww.). Hang in there, I'm hurting with you.

-TheQueen RN

Looking back, I did not outright answer your question, I shall rectify. Grab a flashlight and find a mirror that you can easily see your face in. Shine the flashlight down your throat (bounce the light off the mirror) and stick out your tongue. What you should see is very LARGE tonsils and there very well may be yucky whitish stuff on them. That's normal for mono. If there's something else on them, maybe call your doctor just in case, otherwise just wait out the virus. )
Hope that helps.
-TheQueenRN