Any Soft Coated Wheaten Terrier owners?

Looking for fellow Wheaten owners to answer a few questions I have. I used to be a member of a British Wheaten forum, but waited months on end without receiving answers to my questions. Basically, I have a male Wheaten, just turned 1 y.o. in November, who has some digestive problems as well as a skin problem—I know that Wheatens are known for allergies to wheat and chicken. We have completely removed these from his diet since I adopted him last May. His food is an expensive Venison/Rice mix, and we try to avoid table scraps, yet he consistently has severe diarrhea (usually 2–3 times per month for about 3 days each time). He has also been throwing-up alot lately, but that’s probably due to his fondness of eating plastic… In addition to his stomach problems, he is constantly chewing on himself and creating sores and mats (which turn an odd red color?). I have tried changing shampoos, conditions, etc. Any suggestions from those familiar with the breed? Thanks!