Urticaria can have many etiologies, ranging from lupus to a genetic immune disorder to liver disease. Often the precise cause is not found. Assuming you have had the usual screens, you might try homeopathy. You have nothing to lose.
Have you considered getting allergy testing done, to see if your urticaria is being triggered off by something that you are touching or eating?
If you are constantly being exposed to the irritant, then the urticaria will persist. An irritant can be absolutely anything from detergents (I suggest you use non biological washing detergents if you are not already using these). Soaps, shampoos, chemicals that you use in the house, chemicals that you may come into contact with outside, plants, make ups, some foods, drinks, dust mites, animal dander, woollen clothing. The list is endless.
An allergy test may give you some answers or none. But it would be worth asking your doctor to refer you for an allergy test and a referral to a dermatologist.
Don't use normal soaps and any that have perfume in them. Go for the ones that have a pH level like our skin. You may be fine with baby products. Use products that are suitable for people with allergies.
Keep a written list of everything that you touch (include any contact with any plants), eat and drink, etc. to see if you notice when your symptoms get worse or better to see if you can find a pattern that may point you in the right direction to avoid contact with the "culprit" allergen.
As a young person I suffered with urticaria on exposed areas of my body (hands and neck) - I figured out that I had an allergic reaction to the sheep when we walked past them when we walked through an open green area. Another time whilst in my bikini I got urticaria all over my body and figured that was an allergic reaction to the field pollen that we were passing whilst holidaying on the river. Another possibility on that particular holiday could have been the sun lotion and exposure to too much sun.
Best of luck.
Let me know how you get on.
Something to think about - do you have any contact with engine oil or rubber products?
Get rid of the inflammation first. Use Aloe vera because it typically reduce inflammation,redness, itching and pain. Take a cool bath or apply a cold compress. Also, shrink blood vessels with calamine lotion or witch hazel.