What Does Bleeding Of Blood Clots And Old Blood 3 Weeks Postpartum Indicate?

im 6 weeks postpartum i stopped bleed 3 weeks after giving birth and started bleedin old blood 5 weeks postpartum its now 6 weeks and im still bleeding and passing alot of blood clots. and i have string like stuff coming out of my vagina and the toilet water is red after everytime i pee. i passed a clot the size of a golf ball. im not sure what going on. i have not been feeling good on top of everything. could some of the placenta been left in me after my c section??