My chiropractor has told me that the tension in my neck and back, is the likely cause of my chronic sinusitis. is this possible?

Haven't heard that: A chiropractor is not a medical doctor. It is better to see a physiatrist (also known as a Physical Medicine and Rehabilitation doctor) or see an Orthopedic Spine doctor. Always have a primary care doctor to check for general problems, and he or she can refer to the other specialists. For the sinusitis, one's primary care doctor, an ear-nose-throat doctor, or an allergist doctor can help.