allergies ?

Question
I adopted a cat from a rescue shelter 2 weeks ago - his name is Logan and he is approx. 2 years old.  I was told he tested negative for mites, worms and leukemia but that he food allergies, and they thought to "grain".  I have him on Wellness CORE catfood that is high protein, grain free food.  He has been on this for about 1 week.  He grooms excessively and I acts like he is uncomfortable where he can't relax.  He will jump up on the bed, lay down, get back up,groom, jump down, go to another room and do this all over.  I noticed tonight that he has ripped out all his fur on his hind leg - to the point that it is raw and bleeding.
1.  Could his behavior be from feeling uncomfortable due to feeling "itchy" ?
2.  Do you think he has food allergies ?
3.  What can I do to stop him from pulling out his fur ?  Is there an ointment or shot so he stops pulling out ?
I'm about in tears.  I don't know what to do and I don't know enough of his background.  I feel so bad for him and I don't know how to help.

Answer
To answer the question of food allergies, I would advise you to put him on a special food called z/d for 6 weeks. If that stops the itchiness, then it is definitely a food allergy. Usually, however, cats with food allergies have very itchy and scabby areas on their face.  If he is really itchy, then the vet can give a shot of DepoMedrol to stop the itching.