My Tooth Still Hurts After 3 Months?

So, I have asked this question before, but now have more updates and just wondering if anyone out there has ever experienced this.About 4 months ago, a dentist suggested I get root scaling in all 4 quadrants, I got it done, thinking I was being proactive in helping my teeth.

About 2 to 3 weeks after the scaling I woke up and noticed a chip/divot in on the top outer surface of my first pre-molar on the left side of my face, located on my upper jaw. Right near the gumline, where the scaling was targeted.

I went to my primary dentist office where the scaling was done, he inspected the chip, X-rayed the tooth said everything was fine and that he would not fill it do to the position of the chip. He also said it was not related to the scaling.

I went to a secondary dentist after a constant dull pain in the tooth would not subside. At least I believe its that tooth area, cant really tell, I have had the pain so long some days I just don't know anymore. The second dentist X-rayed, so tooth is fine internally, and filled in the cavity.

The pain returned about two to three weeks later and I returned to the secondary dentist, he x-rayed the tooth and saw nothing wrong internally and could not give me an answer why I was in pain.

After about a week the still dull, lingering pain would not stop. I went back to the secondary dentist. He filled over the initial filling believing it was too thin, and also said my gum had receded so there was a part exposed he could not fill (because he would have to remove the gum, and replace it to fill the area), and the pain would be there for around six months for it to heal naturally. Is that acceptable, or a normal response? (did not seem that way to me).

I then returned to this same dentist when the pain did not subside 1 week after the last appointment. Where he literally said he did know why I was in pain and he has never seen this before.

I then made an appointment with an endodontist. She took a high definition x-ray of all the teeth on my upper left jaw. Saw nothing wrong with any of them. Conducted hot/cold, electric, tactile, and air flow tests on all teeth, and had no abnormal responses. She then concluded I may have tooth pain from a sinus infection (I had been sick, but not for the 3 month period, maybe 1 week before I went to see her). I was prescribed a z-pack of antibiotics, bought decongestants. It is now one week after that appointment and I am still in the same amount of pain. A low, nagging, constant pain that isnt excruciating but just enough to take away my concentration from being able to do work, or relax at home.

Has anyone experienced anything like this remotely? Is there any merit to a sinus issue causing the pain? Or does anyone have a clue from the description what other problems may be causing this?