Swelling to left side of face; jaw; neck and behind ear. took to uc and they put him on abx treatment. when will swelling go away?

Soon.: Since you are on an antibiotic for infection you should be seeing improvement within 2-3 days but it may take the entire antibiotic course or longer for swelling to completely resolve. If you don't see improvement within 2-3 days see your primary doctor or go back to the UC for a recheck. There could be many reasons why it's not improving and may need a different antibiotic or I&D. Good luck.