I have only had one c-section (been three years since I had it) and it dose not hurt when I exercise like you described (just the burn from a normal workout which is felt all over). I do yoga, situps, pushups, light weight lifting, and running. Defiantly talk to your doctor about it and make sure everything is ok and things have healed correctly (might need a ultrasound to see the inside, and I would insist that the check over is more then a touch the outside scar area because that does not always tell you what is going on inside).
Usually when there is such discomfort when exercising there is something that needs to be looked into. A good work out might leave your muscles a little sore but never pulling, snapping, hurtful feeling... also make sure you are doing the exercises correctly because you can feel the "bad pain" when any exercise is done incorrectly.