Hello, I Have Been Having Big Swellings Which Are Hard,

hello, i have been having big swellings which are hard, non itchy and painless on my scalp since two months. i saw 4 gps, and they say its allergy. i saw things get worse, if i eat chocolates and cashew nuts. i avoided few foods and was keeping well for 20 days now. last night i had some white chocolates and develpoed same huge hives on the scalp after 12 hrs of eating it. my question is can food alleergies develop after 12 hours of having them? and can chocolate cause allergies?