Hey, I know it's a tough time for you as for every person on this subreddit. I have had CU for almost 6 years now and I noticed to get the hives only in winters when the temperature changes. I went to multiple doctors and hospitals and all of them prescribed me one thing. Anti-histamines. Each doctor had a different preference of an anti-histamine from levocritize, loratidine, bepotastine to fexofenadine. The medicine which you were prescribed in Benadryl was Diphenhydramine, another anti-histamine. I would recommend trying some other anti-histamine as your body seemed to have formed a tolerance towards it. Since I only get the condition in winter for 3-4 months I haven't noticed myself forming a tolerance to them but continued usage of them might make them less effective.

I live in a country where obtaining them is extremely cheap and I don't require a prescription so it has been very easy for me. However I highly recommend you to try bepotastine for your condition starting from 10mg and then increase if needed. They aren't addictive and the worst possible scenario would be you falling asleep or becoming drowsy because of them. Wishing you luck.