I am not sure it's a right group but I have this since 1 year

I am not sure it’s a right group but I have this since 1 year.
After eating i get a skin rush and itching after 15 min usually and than it’s goes away 2-3 hours. My skin get swollen first and than itchy. I went to my GP, he does not want to send me a dermatologist or do an allergy test… only suggested me to look what I eat and than try to avoid if I notice any difference. I try to avoid milk, gluten,sugar … tried several diets.
Any suggestion? I really don’t know what to do… I dont like to eat in a restaurants because I start to itching and it’s so uncomfortable.
It’s mosly on my upper legs, arms, back, chest and face.
Thank you for your help and stay safe