If your tattoo becomes ‘bumpy’, or stands proud of the skin it is usually your body telling you that you are dehydrated. Your skin shrinks and obviously the scarring left by a tattoo will stand proud as the skin can not shrink as well as unscarred skin. The itching will be to do with blood flow to the scarred area and your body asking you to stimulate the area, its a natural reaction kile pins and needles etc.
If you drink lots of fluids (preferably water) it will calm down.