Your detailed description was indeed useful to zero in into your problems. What your dentist
told you is right, I would suggest you to get a repeat x-ray of the teeth as well as the sinuses to rule out sinusitis
. You need to take a second opinion
from a good dentist and a opinion of the ENT specialist
. Many a times the root of the molar tooth can lie in the floor of the maxillary sinus causing recurrent sinus problems.
Dr. Naveen Kumar