5 yo boy w/ painful pea size lump right base of skull, s/s for two days, not red or inflamed, no injury or infection. ... Concern?

Likely lymph node. There are chains of lymph nodes along the neck including at the base of the skull. They can become enlarged with any infection on the scalp, face, or ears... Often they can persist for a while after the infection resolves. If it is still there the next time you see your pediatrician, ask him/her to take a look at it, but most likely it will resolve over the next few weeks.