Why is this happening??

Im 29 sexually active for like 12 years. Until a year ago i never used lube and i never had any issues. After my third child born last November by c section. I can literally only have sex once a week because i literally get frictiins burns around the entrance of my vagina. Like literally burns that are visible wounds like carpet burn which clear up after a week. Also my perinium tears ever so slightly but causes alot of pain. I have added lube to the mix even though i have no problem wth dryness and it helps a little. Why is this happening? And now? Please help!!

Ps It is not due to any type of infection