What Causes Hard Bumps On A Tattoo?

I got a tattoo july 3rd 2010, and i got my bestfriends ashes put into the ink. Every once in a while, starting like three months ago I keep getting these hard bumps that hurt where the ink is in some places and a hard thing and some liquid comes out of it. Is it a health issue I should go see my doctor about or is it due to the ink or my body rejecting the ash? Im worried