Irritable Bowel Syndrome (IBS): This condition is often exacerbated by hormonal changes, which could explain why symptoms worsen during menses. The fluctuation in hormones can affect bowel habits and sensitivity, leading to pain during defecation.

Constipation: Hormonal changes during menstruation can lead to constipation, which may cause pain during defecation.
Hemorrhoids: These can be exacerbated by constipation or increased abdominal pressure during menstruation, leading to painful defecation.
Endometriosis: Although not exclusively related to bowel movements, endometriosis can cause pelvic pain that may worsen during menstruation and could potentially involve the bowel, leading to painful defecation.

Ovarian Torsion: Although rare and not directly related to defecation, ovarian torsion can cause severe pelvic pain that might radiate or be referred, potentially worsening during menstruation. It's a medical emergency.
Ectopic Pregnancy: Similar to ovarian torsion, ectopic pregnancy is a medical emergency that can cause severe pelvic pain. While it's less likely to be directly related to defecation pain, the severity of the condition warrants its inclusion as a "do not miss" diagnosis.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease or ulcerative colitis can cause painful defecation and may have exacerbations during menstruation due to hormonal influences on the bowel.

Colorectal Endometriosis: A rare condition where endometrial tissue grows in the colon or rectum, potentially causing cyclical pain during defecation that coincides with menstruation.
Intestinal Obstruction: Though very rare and usually presenting with more dramatic symptoms like severe abdominal pain and vomiting, an intestinal obstruction could potentially cause pain during defecation if partial and intermittent.