Polycystic ovarian syndrome. Essentially, my uterus started making little cysts for fun and also my testosterone went way tf up and bad things that accompany high testosterone happened so I didn't have my period for six months. The male doctor said "oh you're just pregnant, get some bloodwork to confirm, and also you need to start taking prenatal vitamins" despite the fact that I had taken multiple pregnancy tests that were negative and hadn't had unprotected sex in that time period.

Fun fact: PCOS affects an estimated 6–13% of women of reproductive age, and up to 70% of cases are undiagnosed. (WHO)