One possibility is contact dermatitis to metals or other materials. Contact dermatitis is a delayed allergy and antihistamines would not be helpful. Symptom may include eczema, skin inflammation, and/or itching.
Poison ivy is also a type of contact dermatitis. An allergist can test for contact dermatitis with a test called patch testing. This involves placing patches (kind of like stickers) on your back. These have several different allergens. These are typically worn for two days, removed and then the skin is reviewed again the following day to look for eczema under the patch to determine which allergens are triggers. Nickel and cobalt are common metal triggers. Titanium is often at lower risk for a reaction. Getting a consultation with a board-certified allergist would be a good first step.