Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
1
Is any of this happening now?
Call 911
Seek emergency help if you may be pregnant and have bleeding with severe one-sided pelvic pain, shoulder-tip pain, marked dizziness, or fainting.
These can be symptoms of an ectopic pregnancy, in which a pregnancy develops outside the uterus.
Emergency assessment is also appropriate if you soak through a pad or tampon every hour for more than two hours and have dizziness, faintness, chest pain, or shortness of breath.
And for anyone, someone who:
is bleeding heavily and it will not stop with firm pressure
Other emergency signs, for anyone
Someone who is struggling to breathe, gasping, choking, or cannot get words out
Someone who has chest pain, tightness or pressure lasting more than a few minutes
Someone who has sudden weakness or drooping on one side of the face or body, slurred speech, or sudden confusion
Someone who is unconscious, or cannot be woken
Someone who has had a seizure that will not stop, or does not wake up afterwards
Someone who has lips or skin that look pale, blue, grey or blotchy
Someone who you believe has taken an overdose or swallowed something poisonous
2
Is any of this happening?
Be seen today
Contact a healthcare service the same day if pregnancy is possible and you are bleeding, particularly if you also have pelvic pain.
Seek prompt advice for very heavy bleeding, worsening pain, fever, or feeling unusually weak.
3
Does any of this apply?
Book an appointment
Arrange a routine appointment if:
You have missed three periods and are not pregnant
Your cycles repeatedly become unpredictable
Bleeding occurs between periods or after sex
Your periods become much heavier or more painful
You have tiredness, breathlessness, or other possible signs of anemia
Irregular periods occur with major weight changes, nipple discharge, or increased facial hair
You are having difficulty becoming pregnant
Bleeding returns after menopause
Every sign above is quoted from the sofidex article on Irregular periods. If you are not sure, err upward — it is always reasonable to be checked.