Hello,
Chances are you have bruised a muscle in the rib cage. These muscles are known as intracostal muscles and they are easily twisted or pulled in the wrong direction and that hurts like the Dickens. One of the best things you can do is to initially put a cold compress on the region for about 15 minutes. Wait 15 minutes to a half an hour and apply a warm compress. Repeat this during day and early evening. The next day I would just use a warm compress because it feels the best. When sitting make sure you sit erect and not slumped because this will make you muscle hurt more. When you sleep at night, sleep on your back and your bed should be fairly hard. You don't want you bottom to be sunken down in the bed. Put a board under your mattress if you have to. Give yourself about a week and it should clear up.