Hello there If its just a sprain as seen in the xray, The cause for your pain now is you didnt take adequate rest to the part as your pain was brought down by medicine....rest to the part is necessary along with cold application or hot bath and gentle stretching....also most common for seatbelt injuries is bruised rib...which is injury to the cartilege...that will cause u a lot of tenderness. What are your present symptoms now? Whixh movement causes pain? Do you get pain on deep breathing? Do get back online with answer for the above questions for proper guidance and furthur advice. Regards.

You should wear a rib belt for few days and go to physio for hydro therapy it will help to decrease ya pain.