biting own fur out

Question
I have a 14 month old male sealpoint siamese tom that has been losing fur on his back in a even pattern,middle back area.  Consult with vet,injections for hair regrowth three weeks ago but just more hair loss.
Two days ago while I was sitting on the sofa he came and sat at the end and started to bite the fur out spitting and biting more out.
I sounded stern and said Ziggy then he looked at me and snorted like he does when he disaproves of anything I reprimand him with.
Fur loss started-mate came in season since then she got sick and had to be put to sleep then stupidly I replaced her thinking it might benefit Ziggy, he gets on alright with her though a bit too rough at times and we trie not to intervene,  

Answer
Hi Kate,

I have never heard of hair loss injections, is this something new?   It sounds like a nervous thing to me.... perhaps the loss of his mate?    

Blood tests will tell you if it is a major problem causing hair loss such as problems with liver, pancreas etc, but these tests can be costly.   

It it is an allergy, the vet should be able to give a shot for that.....

I wish you the best... I'm really not sure how to tell you to stop this behaviour.....lots of attention and maybe some catnip toys might take his mind off it.

God Bless,
Becky