Why does my c-section scar hurt?

I had my second c-section 9 months ago and every time I carry something heavy I am in so much pain down where my scar is and I will be sore for a day or two. (For example after I carry in a lot of grocery bags or today I wore my son in a baby carrier) I don’t remember hurting still 9 months after my first c-section. Should I call the doctor or is other moms experiencing this as well? Thanks!!