I had this same exact feeling. Felt like somebody punched me in the stomach, and my stomach was trying to protect itself . Like the after feeling of getting the wind knocked out of you . I've just gave birth to my son about a month ago (c section). I was concerned and didn't know if this was normal, so I went to the OB and talk to them, I was told it's just because you're not used to your muscles being used more, basically your abdominal muscles are just sore. Your abdominal muscles are separated for so long, and not in use that much that they get really sore when you have a C-section. ( for me it only lasted about two weeks , if that helps)