I have a pain in the right shoulder blades / rhomboid. happens when sitting or walking. goes and come back (6 months now) why? i'm fit + exercise btw

Laying on sides?: It difficult to give you sound medical advice without a proper history and physical. The symptoms you are describing could be indicative of multiple medical problems. But sleeping on your side or watching TV in a reclined position like from your bed or a sofa may put lots of pressure on the upper back, interscapular and posterior neck muscles that may eventually cause trigger points.