Perhaps further - along with adding in only one animal product at a time, try adding it in incrementally larger amounts, starting from a rather small one.
I have done a couple of 10+ day fasts on nothing but fresh lemonade, and when I added back solid food all in a rush once, it all hurt, even though it was completely safe food my system had eaten just 10 days before. I think this is comparable. Next time around, I did it gently over a couple days and - much better. As long as you aren't exhibiting symptoms that are way out of line, like hives, shortness of breath, swelling of limbs, and all that, take it slow and easy. There is no real rush here.
I have a mantra that I have spouted for years... "If I eat right, I feel right. If I feel right, I exercise right. If I exercise right, I think right. If I think right, I eat right..." Phil-SC