You have a few possible things going on here. First, I can't believe they treated ringworm w/ just a shampoo???!!! YIKES. It's usually treated w/ Diflucan x 6 full weeks, then you retest the skin by growing out a skin scraping in culture for 10 days. To me, it sounds like it's either not gone (bc it was never really treated in the first place) or - he actually has pyoderma, which is a skin bacterial infection that results in red patches and itchiness.
Allergies of any kind would be VERY rare and nearly unheard of in an 11 mth old dog. The paw licking and itching does point to it though. Food allergies are very rare. You could try switching to something else and seeing what happens - no harm in that...I'd recommend something like Natures Logic Venison kibble or something.
Giving Benadryl 2x a day won't do enough, it needs to be giving 4x a day due to its short half life. Benadryl almost never works well for allergies in dogs, it's just not powerful enough.
For more about how to approach allergies, read this:
http://www.yorkietalk.com/forums/die...tart-here.html