Since October I Started Having Tooth Pain, Sensitivity To Eating

Since October I started having tooth pain, sensitivity to eating or drinking anything cold on my left side only. Went to dentist, had X-rays done and nothing was found, referred me to endodontist for possible root canal. He took X-rays and did extensive exam and found nothing. Still having pain that has worsened, went to my doctor thinking I had sinus infection. Was put on antobiotics but pain stiil there. Since then did have 2 more sinus infections and was treated. Pain is still there, the only thing that brings relief is Advil. I have noticed that when pain is there and I floss my teeth, the gum between my teeth is hanging lower than when the pain is not there. I am at a loss and still in throbbing pain.