Suggest Treatment For Weakness In Shoulder

Hi, my right side shoulder feels uncomfortable. I injured it in the gym a while ago. At the time I couldn't move it for a week. Then the pain went away and it's been about a year that it feels uncomfortable but there is no pain. I feel like it's not where it suppose to be near the blades on the back. For example whenever I excercise, let say like bechpress, my friends tell me that my right arm is little lower than the left an to keep it even. Also my right arm should be stronger but because of my shoulder it's weaker than my left. Any suggestions of what's going on an what I should do?