Pain that comes on suddenly and is severe
Period cramps build over hours and ease with heat or painkillers. Pain that arrives all at once and keeps climbing is a different thing — it can mean an ovarian cyst has ruptured or twisted (ovarian torsion), which cuts off the ovary's blood supply and is treated as a surgical emergency.
Go to the emergency room. Torsion is time-sensitive: the sooner it's untwisted, the more likely the ovary is saved.
Soaking through a pad or tampon every hour for two hours or more
That is roughly ten times a normal flow rate. Sustained bleeding at that level can drop your blood volume faster than your body replaces it, which is why it comes with dizziness and a racing heart.
Go to the emergency room, and don't drive yourself if you feel faint. Passing clots larger than a golf ball, or bleeding that soaks through your clothes and bedding, counts too.
Fever above 38°C / 100.4°F together with pelvic pain
Fever plus pelvic pain suggests an infection that has moved up into the uterus, tubes, or ovaries — pelvic inflammatory disease. Untreated, it can scar the tubes within days and cause lasting fertility damage.
Get seen the same day — emergency room, urgent care, or a same-day clinic appointment. This is treated with antibiotics, and speed is what protects the tubes.
High fever with a sunburn-like rash, vomiting, or confusion while using a tampon or cup
This is the pattern of toxic shock syndrome. It is rare, but it moves fast and gets dangerous within hours, which is why it's on this list at all.
Remove the tampon or cup and go to the emergency room now. Say the words 'I've been wearing a tampon' — it changes how quickly they work you up.
Fainting, or nearly fainting
Briefly greying out at the peak of a bad cramp happens and isn't usually dangerous on its own. Actually losing consciousness, or feeling faint alongside heavy bleeding, means your body isn't keeping enough blood to your brain.
Get to the emergency room. If someone lost consciousness and didn't come round within a minute, call 911.
One-sided pain with a positive pregnancy test, or with a late period and any bleeding
A pregnancy growing outside the uterus — usually in a fallopian tube — cannot continue, and can rupture the tube. Shoulder-tip pain alongside it is a warning sign of internal bleeding.
Emergency room, today. Tell them your last period date and that a pregnancy test was positive, or that you aren't sure.