postpartum bleeding

I gave birth 9.2.16 to twins. It'll be 6 weeks this Friday and I'm still bleeding. I went for a checkup at 3.5 weeks PP and my doctor went ahead and did a Pap smear and inserted my nuvaring. I ask because before he did that my bleeding had lightened up and was almost gone then two days after I started bleeding heavy again and it hasn't stopped. Do you think the nuvaring has irritated something causing me to bleed still? When did everyone stop bleeding and when did you have you first period after giving birth???