Has anyone experienced this?

I'm 3 weeks postpartum and we had sex yesterday. I had like all but stopped bleeding like it was the faintest pink and barely any. Now the blood is back to the red and its like period amount.....have I done something wrong....no cramps or pain just bleeding is back.....kind of like if you have sex when you think your period is over and then you bleed for another day or two?

Update: the doctor had asked if we were already having sex at my 2 week checkup......my csection has healed really well and we weren't rough. Plus they had already started my birth control at the 2 week checkup. I went home 2 days postpartum and we went on our first outing 3 days postpartum. I was already back to normal pretty much.....the bleeding isnt severe and it's already lightened up pretty sure we just loosened more of the leftover gunk is all.....