I'm in the middle of this same type of thing. Have been complaining about R sided sinus problems for a couple years. Better w antibiotics. About a year ago developed a bump in the roof of my mouth. ENT performed biopsy for possible cancer. Wasn't cancer, was inflammation. When bump returned 10 days after surgery I asked dentist about it. He thought I might have an abscess in R upper back molar. The abscess was confirmed by endodontist. He found I'm missing bone where infection has eaten through it to form sinus tract into my hard palate. A root canal was done. Still issues, so had incision & drainage of sinus tract. Infection still present so just had another root canal in same tooth in attempt to fix (can't do apicoectomy as roots too close to maxillary sinus). If this doesn't work then he will remove tooth. I hope that'll be the end of it and I don't end up needing sinus surgery or oral surgeon intervention. Wish someone had considered my tooth could be the cause before the infection got this bad.