Ben, did you dive before the symptoms of the ear infection came up?
Barotrauma can look very much like infection. But divers ARE prone to external ear infections, which usually present with pain when you move the pinna, or external ear. Barotrauma, with the accumulation of fluid behind the drum, CAN convert into infection with time. Such middle ear infections are treated with oral antibiotics, while the outer ear infections are treated with drops, unless they don't respond to them, in which case oral antibiotics can be used.
When a patient is first seen, it is important to make a decision as to WHICH kind of ear problem you are dealing with, and treat it appropriately. Unless you had a really SEVERE otitis externa, it was odd to put you on both oral and topical antibiotics immediately.
I agree that you should see someone who is familiar with the issues divers have with their ears. It would be a rare urgent care doc who would have this experience.