Ringing in ear. Or to be worried about.

I have continued ringing in one or both(at times) ear. Consulted ENT specialist twice, he said nothing to worry. He asked if I had cold recently, I had heavy cold and cough in November. His suspicion that it is an aftermath. Was given Allegra for a week and ear drops to clear out build up wax, if any. No relief from ringing noise. Went for a follow up, informed that I have sinusitis and that because of cold weather have been waking up with nasal congestion daily. He took a hearing test, readings normal. He gave a course of antibiotics and nasal decongestant for a week, still no diff. I still feel the ears are blocked, with left been more blocked than the right ear and continued. Please advise on why this could be happening and if it is something serious or to be worried about.