Although it may be bike fit and reach...it may not. This is my second bike, both fitted (I TRUST my LBS guy) and this bike is actually even a better fit. I find that since I work at a computer and get that "hunch" and then spend a LOT of time on my bike I get it flared up now and then. Once it flares up...it is hard to get rid of besides a week away from the computer & stress ( = vacation!) Core work also helps.
Mine does not hurt all the time, but when it flares up it is harder to get rid of. Some folks believe in massage. I usually do some foam rolling. So yes, check out your fit, but for me it is other factors. In fact I am "flared-up" right now and even not on the bike it hurts and is "sensitive" (can't stand stuff on my back touching it). So I should reading TE and typing at computer!
Not sure if this helps or not. Just you are not alone.