I did a couple of hours of surfing on this and came up with the following links
This one seems to describe what you are going through.
This
US article gives a lot more detail.
However I did a bit more digging because I was trying to find out why my doctor prescribed antibiotics and why it worked for me.
I found this
NHS Article about the treatment of Helicobacter infections and the impact on Urticaria. I can understand your doctors hesitancy about Antibiotics because Antibiotics have been defined as a root cause of urticaria. However, you as well as I, understand the whole concept of "root cause removal" and "issue mitigation". Using antihistamines to treat a histamine related reaction to a condition is nothing more than treating the symptoms until the root cause goes away. Treating the root cause removes the symptoms.
If you do have a Helicobacter infection, it might be worth trying to convince the GP to do the microbiology tests and then treat the Helicobacter infection if you have one.
Just some thoughts. Hope it helps the understanding. The point in the first article about acupuncture and some relief may be useful. I don't know. I remember just how awful this was when I got it at 18. I know I'd try anything to get rid of it.
Interestingly every article says it only becomes acute after 6 weeks. I.e. most of them go away in the 6 week window. Cold comfort I know.....