What kind of otc medication can i use to treat eustachian tube dysfunction? (already using flonase)

Keep using it: In the right way, directed backwards and outwards towards your ear away from the midline to avoid the nasal septum and to spray the nasal cavity well back to the where the Eustachian tubes openings are. It also helps if you irrigate your nose regularly with saline before using the flonase, if no improvement see your doctor/ENT, good luck