what should i do ?
Nothing really you can do if the diagnosis is correct except rest, ice and anti-inflammatories. The problem is if you don't lay off of it for a while it will become a constant recurring injury. When the muscles and tendons become injured they become imflammed and with the limited space between the humerus and acromion (upper head of the arm and the top of the shoulder blade) it becomes irritated as well as the surrounding tissue.
Rest, ice, anti-imflammatories.