Tenesmus. Tenesmus ("dry heaves of the rectum") can be due to lots of causes. Irritable bowel can do it. Inflammation in rectum causes spasm whenever stretch due to gas, solid or liquid stool passes through. Can also be due to pressure from gyn organs, colon or rectal masses, including hemorrhoids (and cancer). See your doc.
Rectocele. If you are really a mom of 23, I salute you! Seriously, you could have a rectocele- a weakness of the tissue between the vagina and rectum. This can cause a ballooning of the front rectal wall and cause difficulty with bowel movements. See you gynecologist. In the meantime, try adding a daily fiber supplement like metamucil.