Hey there, I'm sure it is prob just the scar tissue streaching, it is full of much more long collogen fibers, and is less streachy than the surronding un-scared skin.
One of the risks after having a CS and becoming pregnant again is a uterine rupture (tiny risk statistically 1 in 500 = 0.02%) . This is where the uterus will tear at the scar site, usualy because the tissue is unable to withstand the pressure of labour. If it does occur, it usualy goes slowly, in labour or (even rarer) in very late pregnancy.
You would feel pain over the area (more internal, not on the surface of the skin scar) that is persistant, swelling over the scar, and a rise in temperaure.
If your scar has been itchy and you have been scatching it, or if it is chafing on your underwear it would feel hot to the touch - this is the most likely explaination.
Talk to your MW about it - you can always call 24hours a day if you are worried. Sometimes the best medicine that healthcare professionals can offer is reasurance. So don't worry about it disturbing anyone, or being embrarassed, or anything else that would stop you from seaking help.
XxX