Why does my tattoo get lumpy?

I Had my first tattoo about 4 or 5 yrs ago,i have 4 now,but the one i had done second (abut 3yrs ago) sometimes gets all raised where all the outline is,it gets itchy red and then the tattoo goes all lumpy like braille,i can feel what it looks like.Anyone have any idea why its recently started doing this,the others don't