Fluid in ears (middle part of ear) could be becuase of poor Eustachain tube function (Tube connecting middle part of ear and back of nose). Which normally open and closes and maintain middle ear pressure same as outside pressure.
It does not function properly when there is infection in nose, In flight when due take off and landing the pressure difference causes the tube to close, if there is any swelling or mass behind the nose like enlarged adenoid
or any growth , and also long term reflux from stomach can cause this.
You can see an ENT specialist
and get done--
Ear examination to see the your ear drums are intact .
Get done Impedance audiometry
-a test to know if there is any fluid behind your ears.
Get done nasal Endoscopy
to see the part behind the nose.
TILL THEN PREVENT WATER ENTERING YOUR EARS WHILE TAKING BATH.
Get well soon.