It is better to have a X-Ray Chest PA View to rule out the possibility of rib fracture. If the fracture of rib is excluded, then it might be the muscle contusion or bruising as mentioned above and you may start the principle of RICE or PRICE for the first 72 hours.
R-Rest
I- Ice
C- Compression
E- Elevation
P- Protection
R-Rest
I-Ice
C-Compression
E-Elevation