I was told that i have endometriosis on my incision where i had a cesarean section. how is this possible?

Scar endo: This is much more common phenomenon than you think. Because at the time of cesarean section the uterus is opened and the endometrium could be in contact with the fat at the incision site, the tissue can implant creating endometriosis at the scar. The symptoms are cyclic pain and swealling somewhere in the scar that subside after menses. The treatment is scar removal surgically.

It is possible: Although somewhat unusual, endometriosis certainly can occur in a c-section scar, or any other pelvic surgical scar for that matter. It is thought that the cells from the inside of the uterus get "seeded" into the scar at the time of the surgery and can then begin to grow, and perhaps cause pain.