Had the same exact problem and was diagnosed with an inflamed disc in my thoracic vertabrae. Only cure is rest and anti-inflamatories. Not saying thats what u have, not a doctor, just relating. Wasn't caused by golf, but definitely aggravated by the repetitive nature of an incorrect golf swing. I tend to hit a lot of balls when I go to the range and as I tire, my swing gets thrown off. Instead of just stopping, I used to try to power through it. That resulted in 4 weeks off of work and 3 months away from golf. Long story short, it came down to the realization that golf is indeed a sport and, unless you have killer genes, sport specific flexibility and conditioning, as well as the common sense to stop when it hurts
(not my strong suit!!)
, must be maintained.