Hi Megan,
I don't know if I can exactly answer your question, but I did want to explain a little more about what you are feeling as "scars." There is a lot of scarring that can happen in a c-section; for certain, you will have one incision scar on your uterus, and one on your skin. There are also other types of scar tissue that form, including adhesions (areas that become fused together that shouldn't be).
The incision on your skin doesn't really "line up" with the one on your uterus -- the skin can be cut much higher or much lower, or even in a different direction than the uterine incision. Also, the incisions are made when your uterus is fully stretched out, but after pregnancy it has shrunk and slipped back down into your pelvis. It might help you visualize where your incision is if you know that it is usually just above your cervix. Between the skin and the uterus, you have several layers (fat, muscle, bladder, etc.); hidden under all of this, you cannot feel the uterine scar from the outside. Here are two diagrams that show the standard incision types; each physician has their own preferred method, which may include a variation of one of these:
http://members.truepath.com/bgadland/incision.html
It's more likely that what you feel under your skin incision is simply scar tissue in the fat layer. It may shift around depending on your weight and on your pregnancy status, as you noticed. I don't think there's a standard time when things shift, as some women's don't change at all -- mine has never done so. BTW, you can work on reducing the scar tissue with massage -- using castor oil packs can also help soften and reduce lumpiness, etc.
I hope that's helpful!
