Is it muffled? Does the inside of the ear hurt when you pull down on the ear lobe? If so, you might have a bit of inflammation in the ear drum. Alternatively, you might just have some catarrh in the eustachian tube. If you swallow really hard, does it click? If so, then the tube isn`t blocked which is the main thing. If you`re worried you could always go to a walk-in centre and get someone to look at it with an otoscope so you can see what the situation is and start drugs if it`s otitis media.