I remember having similar pains hun and I think the thing is that the whole stomach has been through mega trauma with a c/s. If you had it beforehand as well, maybe a muscle was damaged or something like that? Although it was 3 weeks ago, you may have pulled a muscle or something, or it could just still be muscles moving back and healing after the surgery. Does it feel muscular? Have you been doing more than you should be because you feel ok?! I did that a few times - even things like lifting your arms up high above your head can cause it. I also had a 6cm muscle separation so just be careful with what you are doing and if it seems to get worse then maybe call your hospital.

ETA: Just realised how unhelpful my post was Hope someone who has a clue pops in soon for you, and in the meantime I might call it a night! oxoxo