Welcome @jodan, I know it has to be frustrating not to know what is causing the cold urticaria but from what I've read it's a rare condition and there doesn't seem to be any known causes. Here are a couple of articles that provide more information including standard therapies and treatments:

-- Cold urticaria: https://www.mayoclinic.org/diseases-conditions/cold-urticaria/symptoms-causes/syc-20371046
-- Urticaria, Cold: https://rarediseases.org/rare-diseases/urticaria-cold/

How long have you had cold urticaria?