I think its probably normal, because the stretching of that scar tissue can be painful. Its not the uterus stretching, that you're feeling, probably. I'm guessing its the skin and any trauma that occurred to the muscle tissue in that region during the section. I'd recommend a belly support belt, if you can get one. Motherhood Maternity sells them, for sure, but you can get them online. You might be able to get one covered by insurance if your provider can prescribe it. Otherwise, I'd give the physician a call to see if there is anything (other than oral pain meds, of course) that they can do for you.
However, I'd check with your practitioner just to be sure, because if the pain is really localized to one area of the scar, there might be a retained nylon suture or something in there that is causing the pain. You just don't want to be miserable, I'm sure!