First off you don't have to eliminate animal products for the rest of your life, although at first you'll have to go near-vegan until you detox. I still eat eggs, cottage cheese, and fish occasionally and could probably start eating more now, but like being mostly vegan.
It seems consistent you have leaky gut also with you being allergic to everything. Read some of Anthony's posts. He had a lot of the stuff you have. He healed his problems from eating high carb/low fat & protein, but staying away from grains until his intestines healed. Stay away from dairy too.
To maintain weight, you need at least 3,000 calories a day for a male (more for being very active or very sick/stressed because stress makes your body use up more calories) and most importantly, getting at least 5 grams of carbs per your healthy body weight a day for energy and mental clarity. Most people who are under-carbed have a lot of emotional and mental problems, such as anxiety, depression, and general lack of concentration and they start making poor choices.
Your staple for calories has to be either mostly from tubers (e.g. potatoes), starchy vegetables, or fruit. It's a little trickier going low fat because fat has 45% more calories than carbs, so you'll have to eat a lot more carbs to make up the difference, which can be fun if one likes so to eat a lot like me!
If you have a juicer, that would be good to start your detox as it's easy for your body to absorb and gives your body a break from having to process all that fiber. If not, I recommend making green smoothies with a blender. They are a lot easier to make and absolutely delicious and satisfying! I have one just about every morning.
The two diets I recommend to look into, although you don't have to do them strictly vegan are:
The Starch Solution (Dr. McDougall)
80-10-10 (Dr. Doug Graham, an avid athlete)
There's a lot of videos on youtube about those diets and some forums about these diets to further help: