What Causes Severe Pain In The Throat On Swallowing?

Hi! I hope somebody can give me an idea what is up. For a few weeks now it has been painful for me to swallow. The pain is on the left side of my throat and appears to be much worse when I am looking down or to the left. It sometimes feels like it is radiating into my left ear. It seems to be accompanied by a feeling of being very tired as well. I have been to a medical clinic and was told that my throat appears clear. I have been using Nasonex, saline and Advil Cold&Sinus religiously as instructed, to no avail. Any suggestions?