lump on back of head

hey everyone,
Yesterday I found a very small lump on the right side of the back of my head. its right off the neckline about as high as the center of my ear. Its the size of a pea, and its hard. And honestly it was kind of aggravating me cuz it was there so I picked at it a little....prolly not a great idea but now its red and sore but Im guessing that is my own doing. Before that it was not hurting. Im just curious if anyone can shed any light on this as to what it is? should I get this checked out fast or should I wait a few days to see what happens. I also have a small lump on the back of my left shoulder but its been there for ages and never got any bigger or did anything really, so Im kinda thinking this might be the same thing but being on my head is worrisome lol so I thought I'd ask.
Oh well Your Input is all greatly appreciated :)
Thank you for taking the time
Raoul Duke