Sounds like havent been taking care of your tat. Firstly use baby cream on it like bepathen , just a smear 3 times a day for a few days then see if that helps, itching is usually caused by either the skin drying out, or a skin infection, it usually only itches for a week at the most. Again get to the drug store and get the stuff you use on a babies butt with antiseptic in it. Remember with any new tattoo you have to be careful with it, like just pat it dry after a shower, use bepathen for a week on it, keep it covered out in the sun and you shouldnt have any trouble with it, but they can dry out and go scaby but dont pick at it, let it heal on its own.
There are possibilities that your tattoo is reacting with your skin. Normally, a tattoo takes two to three weeks to heal. Seek medical assistance from a dermatologist for a closer look at your skin and he will be in a good position to advice accordingly. For more information, visit; http://poundedink.com/how-long-do-tattoos-take-to-heal/.
If the tattoo was on a spot they had to shave could cause it to be very itchy until the hair fully regrows in. I had this issue and the itchiness was almost unbearable. Trying slapping the tattoo....it takes the edge off the itchiness. Just make sure you don't scratch.
if there's red in it that could be the problem, if you have other tats and have had no problems it could be that your body doesn't like the red or it was old ink I had this happen and I had the tattoo redone and it finally healed