uklocations You may have what people call "patulous eustachian tube" where the tube is open to the middle ear all the time....water will be able to freely get into your middle ear through the back of your nose / throat if this is the case. I am sure you would already know it though as you would have additional symptoms.....
Alternatively, you may have a perforated eardrum - a small hole that is letting water into your middle ear through the drum whenever you get water in your (outer) ear. Either way, a good ENT guy will be able to help you diagnose your problems......if I were you I would stay out of the water though!!!
All the best and good luck solving your problems!