What Causes Pain In The Shoulder Blades?

hi ive been getting a lot of pain in my shoulder blades and tend to get acid coming up my chest. i was told by my doctor that ive got acid reflux which was a few years ago now. but when i drink water i get the pain in my upper back. ive just got back from new york and i was eating a bit of junk food while out there and i do get get constepated now and then. was just asking if this could still be the acid reflux. thanks