Except for showers
There's a connection tube that connects the mouth, nose, and the ear (Eustachian Tube). It's normally wide open in babies (that's why babies are prone to ear infections) but closes at childhood. Maybe yours is still a bit open?
If this happens often, I suggest you inquire about it with the physician. They might be able to do something about it.
Maybe you are congested? It could be a head cold, sinuses, etc...
I suggest you either visit your doctor, or try some Mucinex (or something to get rid of congestion).