I Have A Small Lump Under The Scalp At The

I have a small lump under the scalp at the back of my head near the base of the skull. It very much feels like a bruise, but i haven't hit my head. This swelling presented itself 5 days ago and has progressively become more painful to the touch and occasional sharp pain emitted without being touched.
I did walk through a spider web 5 days ago, but did not see a spider nor feel a bite.
I also have developed 3 other irritations under the scalp more descriptive of a small insect bite that are painful to the touch. None of these swellings itch.