Hi. Thanks for your query. Noted the history and understood the concerns. Stomach flu and bronchitis with completion of Z- pack indicate that you had viral infection and hence the whole body gets affected. Thus the likely affection is by costal area of ribs. This is called costochondritis. The likely helpful treatment is by the following ways: Anti-inflammatory medicines with painkiller properties. Rest to the area by avoiding all activities that put strain on such area. If required apply strap skin adhesive tapes in expiratory position. Of course most important is the EKG as the pain is left sided and cardiac checkup as needed.