I started exatly the same way. My endodontist thought it was either an infected salivary gland or tmj. Turns out my jaw sublaxed (one side came out and protruded on the side by my ear) and my condyle was not moving correctly so I overworked my muscles. My upper jaw was not closing correctly accounting for the pain under the cheek bone. You need to find yourself a tmj specialist who deals with head, neck and facial pain to see what the exact cause of your muscle enlargement is due to. Sometimes they are also called maxillofacialists or neuromuscular dentists. An orthordontist who specializes in tmj is also good. You will probably need to have an mri or sonogram done to look for any abnormalities but they should advise you regarding this. I am sure others on the board with more experience will have more recommendations since I am only a novice when it comes to this. Try some ice packs and over the counter pain relievers for now (I find Aleve or Advil works well) and if it progresses to your neck and shoulder area see a chiropractor who also knows about tmj. Good luck.