What Causes Post Coital Bleeding During Postpartum?

Hello, I am eight months postpartum and have have returned to regular menses. I am experiencing post coital bleeding, the current episode has lasted four days and requires 2/3 pads per day. This is the heaviest episode but I have previously experienced small amounts of PC bleeding. My smear was done 2 months ago and was normal as we re swabs taken at that time. I am still breastfeeding and had my baby by c section with no complications. I am 25 and have only had 1 sexual partner - my husband. We re using condoms, I had my last period 2 weeks ago. I m not in any pain and feel well. I am otherwise healthy and active. Any advice gratefully received.