I'd be more inclined to think that is frozen shoulder if you can only lift it so high with both adduction and abduction (in and away from the body). Typically a rotator cuff injury requires a strain or traumatic event to occur. Most times with frozen shoulder it's unknown how it occurs, except to say that that arm does not get enough movement to it. With blood clots, there will typically be an accompanying redness in the area but movement is not a real issue since it hurts all the time instead of just with movement. Good luck!
I hope it's not clots,doese it hurt in joints or in upper shoulders,cause if it in joints than most likely authritis in the joints,if it's in shoulder area could be torn rotatercuffs. ,stay w,/u'r appointment,I wish u the best