Chicken is a big issue with some dogs and is likely one of the sources of your problems. Do some research on "leaky gut syndrome" as I would be pretty sure this is what you are dealing with. I had a yellow lab years ago that had issues similar to what you are dealing with. Ge the gut back in balance and that should help a lot.
I also used Nzymes products which also helped. I use their probiotics with my current Labs. Allergies in Dogs, What to Consider - NZYMES