Hello there....., it could be due to intercostal muscular spams..... A sudden twist of the chest area may cause an Intercostal Muscle Sprain..... Intercostal Muscle Sprains can be categorized as mild, moderate, or severe. Mild form of sprains can heal in two to three weeks. The moderate form of sprain takes around six to seven weeks to heal..... Take Adequate rest, Apply ice to the affected area, Cold compresses, stretching exercises... Consider muscle relaxants....