Beagle can't stop itching.. Please Help!

I have a 5 year old beagle Tanner who started itching when he was about a year old.  He chews his feet and cries continuoulsy.  I feel so bad for him....  The vet first put him on predisone, it did help for awhile.  So then the vet put him on Temrail P.  Once again it help but breifly.  Then we tried Atopic.  No luck!   So then I tried a number of different dog foods from grain free to raw diet.  I have tried benedryl, Fish oil, flax seed oil, Apple cider vinegar, Grape fruit seed extract,  oil of oregano and so on.  I am currently feeding him raw elk and still no luck.  Last year was the first time I started him on a raw elk diet and it did seem to work better then anything else but he would still itch just not as bad.  Then we ran out of elk.  So I put him back on grain free Duck and potato.  About a month ago my husband got another elk and so we have been feeding him the elk again and have not seen a difference in his itching at all.  It seems that it keeps getting worse every year????  I did take him to a different vet for another oppinion and he said we have tried everything he could think of...  Any suggestions??

Thank you!  I have not tried brewers yeast.  How much do u reccomend me give him??  I'm headed to Mexico October 15th