I had the exact same thing. You probably have an AC seperation. It took me a long time to figure out, when I had it. It is when the ligaments that attatch your scapula to your clavicle ,stretch or tear. There are three types, and even the worst very rarely needs surgery. I couldn't bench for almost a year, although other exercises were Ok. If possible go see a physio, they can give you some exercises to help you out. I cannot even tell I was ever injured, it's been 2 years