I have a fibroid on the posterior exterior uterine wall. is this why i have to push up on my peritoneum to have a bowel movement?

Uterine fibroid: Possibly a contributing factor depending on its location on the exterior wall. Also if you have had children and are perimenopausal/menopausal there is less tone in the perineal muscles and there may be a mild rectocele prolapse ( rectal tissue pushes vagina) so stool gets stuck. Consider trying Kegel exercises to strengthen the perineal muscles. Discuss rectocele with gyn.