Hmm. Sounds like you're allergic to something. Start journaling what you're eating and reactions.
Do you get welts every time you eat?
Are the welts in the same place each time? Do you get them all over?
Are they like hives? I get welts/hives on the fingers of my right hand occasionally. I have always attributed them to some type of adrenal-related reaction.. since my adrenals are sometimes weak'ish. I've heard (can't remember where) that adrenal related hives are the result of not eating balanced meals. Not sure what to make of that though.