any pain?
usual suspect is a blockage of the eustachian tube , stops the ear pressure equalising.... if there's an infection in there, you get fluid build up as well, which effectively means you lose everything bar very low frequency (bass) , if unbalanced (only one ear) then it sounds to you like losing all hearing in one ear...
if you've had a cold and used decongestants of any kind, it's likely the dried up mucus has formed a blockage .
see quack, and if they can't see a damn good reason, do not spend a month of antibiotics.... get yerself to the ENT specialist pronto..... do not prevaricate, or accept moany excuses about not being that serious .....
it can be many other things..... in my case it was a tumour...... which they removed pretty damn fast once ENT had spotted it.....
anything like that James, do NOT dick about, get it sorted, get it done properly, and do so right fekking now