Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Get emergency help if severe pelvic or abdominal pain occurs with:
Seek urgent medical advice for sudden or severe pelvic pain, especially if it is different from your usual symptoms.
Urgent assessment is also appropriate when pain occurs with fever, repeated vomiting, a swollen or very tender abdomen, or significant vaginal bleeding.
These symptoms do not mean that a serious condition is definitely present, but they can occur with internal bleeding, ectopic pregnancy, ovarian torsion, or another problem that needs prompt care.
Arrange a routine appointment if pelvic pain keeps returning, affects daily activities, or has not previously been assessed.
You should also seek routine advice if pain lasts longer than one or two days, occurs throughout the cycle, or comes with unusual discharge, pain during sex, urinary symptoms, bowel changes, or bleeding between periods.
Every sign above is quoted from the sofidex article on Mittelschmerz. If you are not sure, err upward — it is always reasonable to be checked.