Had back&side pain (left), abdominal&hip pain. all since had c section 13 weeks ago, could it be related to pregnancy or recovering?

That is odd: Continued pain as you described is of some concern. You may have scar tissue. There may be some injury to the ureter (the tune from the kidney tintype bladder) which may explain the left-sided back pain though this is not that common in C-sections. Finally, it may be chronic back issues or positional problems even nerve stretching or injuries from the procedure itself though less likely.