How long will my ears feel plugged up?

A week ago I was told I have a double ear infection and was given antibiotics. My ears have felt plugged up and I recently returned to the doctor b/c this feeling of being plugged up in my ears has been happening for 2 weeks now. I was told to stop taking decongestants and he prescribed Allegra, an antihistamine, that should help dry up the fluid in my ears. Here's the deal. I am having so much trouble hearing others that I feel like I'm now hearing impaired. It's terrible. I can feel my heartbeat in my ears but no pain and I'm simply muffled. How long will this last? Will Allegra really help? I'm totally desperate here.