The pain is caused by the pressure that build up of pus behind the eardrum. Your physician has already given you antibiotic (zithromax) and sofradex (anti-inflammatory) to treat your condition. It will take 3 days for the drugs to reach its peak level in the blood and is recommended to continue for a week or it depends on your doctor's advise.
You can have Ibuprofen every six hours to relieve the pain. Take time to rest, avoid scuba diving, swimming, coughing, sneezing, and bending for this could cause pressure in your ears that would trigger pain.