painful lump on side of boob?

about a month ago I noticed a lump on the side of my right boob. its pai ful upon pressure and after a while i forgot about it. well its been bothering me cor almost a week now. cant lay on my right side for long periods of time without it throbbing. its not big, you cant see it, but its definitely there. doesnt help when you accidently lean on it, either lol. any ideas what it could be? i hate hospitals and im really nervous about getting it checked out but I know i need to hwre sooner or later..