I have had these little bumps under
the skin on both armpits for years now... I had my dr. feel them about a year and half ago and he said they are lymph nodes that became that way from me shaving (I do shave quite a bit, and am not known to switch razors when supposed to). anyways, he said that they would go away when I laid off shaving, but I haven't so they haven't really done much either.
They are very small, probably a pin head size or slightly bigger. not a pea size for sure.