Referring to the data you provided (ear infection, fluid in mastoid afterwards, repetitive ear infection), your son might be experiencing mastoiditis. Mastoiditis is an inflammation of the mastoid process, which is behind the middle ear with whom it communicates through a hole in the posterior wall of the middle ear. The mastoid itself is rarely a primary source of infection.


In most cases, the inflammation is spread from the middle ear. The symptoms include pain in the mastoid process when pressure is put on it. Ear pain might also be present due to a possible middle ear infection present at the same time. Nonspecific symptoms like fever and headache can be found, too.


Mastoiditis is treated with antibiotics, because of its bacterial cause. If there is a discharge coming out of the ear, it might be taken for microbiological examination in order to determine the exact bacteria and the most effective antibiotic. In certain cases, antibiotics might not be enough and surgery might be needed.


If not treated, mastoiditis might spread to the surrounding structures. It might even cause repetitive inflammation of the middle ear as might have happened with your son. Other more serious complications include spreading to the skull cavity where the meninges (protective membranes around the brain) might be affected.


You might want to visit an Ear, Nose and Throat specialist for proper treatment.