Thanks for the query.
In case of prior cesarean pregnancy
because of the possibility of adhesions pain can occur when the uterus
grows and stretches those adhesions.
Usually infection will affect the outer wound on the skin. Infection of the inner wounds is rare unless there is history of prolonged labor and/or puerperal sepsis
Uterine scar dehiscence is rare in early pregnancy, so you don't worry but if your pain abdomen increases better to consult gynecologist once to undergo physical examination and ultrasound
which will rule out the possibility of scar dehiscence.