When you say he's allergic to "all foods," are you referring to all protein sources, all grain sources, all vegetables, etc.? He's allergic to bison, elk, duck, goose, pheasant, chicken, beef, fish, carrots, broccoli, apples, etc.? EVERYTHING? That is not possible. Also, all fish are different, so when you say he's "allergic to fish," are you referring to all of them: sardines, white fish, cod, salmon, halibut, perch, etc.?
How much time has elapsed between each type of food you've fed?? Please note that when dog consumes something they're 'allergic' to, those allergens can remain in their system for 3-6 months thereafter. So, if you're switching between foods within a short amount of time, it would appear that they're allergic to everything because they're still reacting to what was fed previously, or before that, or before that, etc.
It takes a lot of time (for some dogs) to work those allergens out of the body. AND, because you were feeding a commercial food prior to introducing noncommercial foods, your dog was likely experiencing detoxification, which can increase any symptoms they're experiencing.
Please refer to the article on this page regarding detoxification & it should clear things up a bit (it is in the middle):