Hello and hope you are doing well.
Looks like he has developed a middle ear infection. There are tubes called 'Eustachian tubes' which connect the middle ear to the throat, this balances the air pressure in the ears. This tube can get blocked due to infections/allergies of the throat, which can lead to a feeling of fullness in the ears. This can also result in infection of the ears. The blocked ears can be opened up by the valsalva maneuver, where air is blown into the cheeks against a closed nostrils, this sometimes helps to open up the tubes. Steam inhalations and warm salt water gargles can help clear the tube. He may need to consult his primary care physician who will examine him and initiate appropriate therapy.
Hope this helped and do keep us posted.
I think he should see his doctor or an ENT. I think you want to treat ear problems sooner than later. Next he may have dizziness or hearing loss.