I am Dr Mbong. The spot/bump/lump may be a million things. :-)
If it is not an ingrown hair, it can be an isolated rash from a bug bite
(when you were asleep or did not notice). It could also be an isolated allergic rash
or the onset of a folliculitis
(boil) or infected sebaceous glands (some glands of the skin). It may also be a zit you got from swimming pool or close contact with someone who had the same rash.
I could also be a thousand other things. Give it time and if it persists, or gets bigger or too itchy or becomes filled with fluid or the skin over it changes color spontaneously or it becomes a wound, see a darmatologist for proper diagnosis.