Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services if swelling affects your breathing, you cannot swallow your saliva, or your tongue or throat is rapidly swelling.
These symptoms need immediate help.
Seek same-day medical care if the lump:
Prompt assessment is also appropriate if you have ongoing hoarseness, one-sided ear pain without an ear problem, unexplained weight loss, drenching night sweats, coughing up blood, or a mouth ulcer that does not heal.
These symptoms do not establish a diagnosis, but they should not be ignored.
And for anyone, someone who:
Arrange a medical appointment if a lump lasts longer than about two weeks, is getting larger, or has no clear connection to a recent infection.
Also book an appointment if it feels hard or fixed, returns after disappearing, or lies just above or below the collarbone.
And for anyone, someone who:
The article also says
Children often develop enlarged lymph nodes with infections.
A child should still be assessed if a lump is growing, unusually large, hard, persistently painless, or accompanied by ongoing fever or poor general health.
Every sign above is quoted from the sofidex article on Neck lump. If you are not sure, err upward — it is always reasonable to be checked.