You mention that it all started of after a certain exercise. What sort of exercise, how long did it take after this injury that symptoms became apparent. Do you only get symptoms during activity or also without.
You have to be far more precise to get an answer: when pain? where exactly is the pain? what sort of pain? Is it only local pain or also e.g in the lower back. Are certain movements causing changes in pain? Have you seen your GP to outrule none musculoskeletal problems? Have you had this before?
Too many options for causes. To name some: Ribs 10-12. Lower thoracic vertebraes and Lumbar vertebraes. Pelvis slightly of position and a muscular injury. The latter as you suggested: obliques injury seems to be rather strange since having pain on both sides (you do not mention left-right)
So you want an answer? Give more information.