According to UTD there is an increased risk of UC flairs during pregnancy. This is weird because the rule is "pregnancy causes these autoimmune/inflammatory stuff to go down" and they love testing the exceptions....

UTD" Fertility, pregnancy, and nursing in inflammatory bowel disease"

• IBD should always be suspected in a young adult without a clear trigger (international travel, etc.) who presents with increased bowel movements, especially if stools are covered with blood and/or patient has associated abdominal pain
• Diseases associated with erythema nodosum = IBD, tuberculosis, systemic fungal infections (cocci, etc.), sarcoidosis, Behcet’s disease, strep pharyngitis (most common trigger)
• Important to distinguish IBD from IBS because both can present in young adults and both can be described as having increased frequency of mucus-covered stools. Features that point towards IBS include lack of blood in stools, abdominal pain that is relieved with defecation and alternating periods of constipation and diarrhea

Ulcerative colitis - young adult, blood/mucous in stools, erythema nodosum

Other answers:

Amebiasis - would expect travel history, liver involvement

Diverticulitis - would expect low-grade fever, LLQ pain, history of chronic constipation

Viral gastroenteritis - would expect watery diarrhea and maybe fever and signs of dehydration

Hyperperistaltic diarrhea - dunno wtf this is but a quick Google search says maybe it's a top secret code for Dumping syndrome