Even though you had a c-section, your cervix is still open. Your husband may be careful, but he's intruducing bacteria into your uterus. Your uterus hasn't had time to get rid of everything in it yet. I would wait until your 6 wks check up before you have sex again. Sex probably caused the bleeding.
I'd definitely let him know. You also have internal disposable stitches that take ages to dissolve.
Ive had my stitches out after 5 days and my cut looks all fine but I feel the blood is different to a normal period blood, I mean its really really red. I go to my doctors to be put on the pill. Should I put it past him then?
I waited the 6wks to have sex but I did overstretch and rip my stitches at about 2wks post partum. Maybe give your dr a call and run it passed them?