What Causes Poor Hearing After Suffering From Sinusitis?

For the past few weeks, I have had some congestion, post nasal drip, and sinus pressure off and on after returning from New York by plane. I already have some high frequency hearing loss, but not to the point of impairment, as I do not wear hearing aids and get by in all situations. Since the onset, though, I have found it harder to hear, even in less noisy situations and I find myself feeling like my head is in a fishbowl. I visited my regular ENT for an audiogram and visit. My audiogram showed no change to my hearing, but less movement of my eardrums than normal. The doctor found no infection after checking me and suggested that it could just be inflammation in my sinuses that he could not see causing this change to my hearing. I am now scheduled to visit with an allergist to be checked for allergies to see if that could cause the issue. I just want another opinion on whether seasonal allergies, inflammation in my sinuses, or congestion in my ears could be causing such a change. If so, is it most likely temporary and how should it be treated?