Hi 'saltine_cracker', my mother has dermagraphism which is a type of physical urticaria. I wouldn't agree with your dermatologist that urticaria is a genetic defect. As for most of the chronic urticaria and the types of it out there, it is usually caused by an underlying condition. It may be an infection, autoimmune problem, cancer(rare)...etc. My mom's dermagraphism has gone and she hasn't have a breakout for a long time! She has frequent UTI and when the UTI was treated, her hives got better. So I guess my mom's urticaria was caused by an infection (UTI).
Your urticaria might be caused by an underlying infection or maybe you might never know the cause. Infections like root canal, sinusitis, UTI can be the culprit. You can use cromolyn cream for the itching. Never scratch yourself if you feel itchy because that will only worsen your condition. Try sponging youself with cool water, some people bathe in oatmeal... Don't be discourage, sometimes the hives will go away on its own. Everyone is different, so no one can tell you when it will be gone for good.
Food allergy test can be done by putting the food on/under the tongue or have the patient swallow it and see if there's any reaction. But it is strictly done at a doctor's office where medical treatment is easily accessible. Blood test, RAST can be done depending on what your doctor wants.
Antihistamines will help to prevent the hives from forming as it stops mast cells from degranulating. However, some patients need more than one type of antihistamine to help them. All the best to you and hope you feel better soon!!!