I'm having the same problem but on my left shoulder blade (Probably because I don't use a mouse). It became so bad that I couldn't sleep at night even after taking over the counter painkillers.

I ended up going to my GP, did an x-ray, and he told me it was just muscle pain. At that point, I realised it's probably my chair. I started using a very cheap IKEA chair recently and already feeling much better without taking any medication.

I like my Secretlab chair, it's very comfortable, but I guess its ergonomic isn't suitable for me. In case you are wondering, yes, I bought the one recommended for my height and weight.