2 Weeks ago I came back from Cancun, where I came down with a bad sinus infection, sore throat, and generally ill feeling. 2 days after my return, I developed a low buzzing noise in my left ear, a sensation of fullness and noise distortion, hearing a lot

Fluid in middle ear. You are describing a blockage in your left Eustachian tube, which connects your middle ear to your upper nasal passage. Sometimes, you can relieve it by holding your nose, blowing and trying to "pop" your ears. You may have fluid filling your left middle ear that may need to be drained. If those symptoms are persisting, see your primary physician or an Ear, Nose and Throat specialist.
See primary or ENT. It is not uncommon for you to have some hearing disturbance with sinusitis or soon afterwards, but it should not last for long. It is tough to tell exactly what is going on without doing a proper exam. If this persists for more than a few days or is bothersome to you, consider seeing your primary doctor or ENT. Best wishes.