Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Seek emergency medical care for:
These symptoms can occur with pituitary apoplexy or serious pressure on nearby nerves.
Arrange prompt medical assessment for gradually worsening vision, persistent new headaches, or symptoms suggesting loss of other pituitary hormones, such as severe weakness or unexplained faintness.
Headache or visual changes during pregnancy also need prompt assessment in someone with a known prolactinoma.
Routine assessment is appropriate for unexplained milk leakage, absent or irregular periods, erectile difficulties, low sex drive, or difficulty becoming pregnant.
These symptoms have many possible causes and do not by themselves mean that you have a prolactinoma.
The article also says
If you are already being treated, contact your healthcare team about troublesome side effects, new compulsive behaviour, pregnancy plans, or a positive pregnancy test.
Do not stop a dopamine agonist suddenly unless you have been told how to manage it.
Every sign above is quoted from the sofidex article on Prolactinoma. If you are not sure, err upward — it is always reasonable to be checked.