I would bet that your sinus problem is your teeth. You mention #12, and #16 in a previous post in the Cavitat forum.
Both are at the top of your mouth near the sinuses.
I used to get 4, or 5 sinus infections a year [for more years than I can remember]. I too was told the teeth were a possible problem. I discounted that information for a couple of years based on the fact that my teeth wern't bothering me. Finally when the AMA doctors didn't have any other answers but antibiotics I replaced the amalgam, and pulled the root canals. Some of which were in the top of my mouth.
Turns out they were puncturing my sinus cavity. After the dental work [About 12 years ago] I haven't had a sinus infection since.
Antibiotics will screw up your immune system with things like Ulcerative Colitis, or Crohns disease. I know from experience.
Do the process of elimination thing. You have no clues except you have been told there is a problem with upper teeth. That's why I suspect the teeth.
Don't do like I did, and slough off the teeth problem.