What Causes Pain In Tail Bone?

I am a 49 year old female and have always been very healthy. I have been experiencing classic sinus infections symptoms (chronic pain in upper teeth, eyeballs, sinuses, top of head, neck and shoulders, burning/cool sensation in upper part of left arm). This has been going on since early January and I have been using nasal steroids, antibiotics, seen a chiropractor, and been to massage therapy. A CT scan for the sinuses showed no infection and an MRI showed nothing abnormal going on in the brain. I am now having problems with the nerve to my tailbone in that it is extremely uncomfortable to sit in a chair for more than a few minutes before I have to change positions and it really hurts. I have been told it's probably stress related - any thoughts?