Hi 'Noct'
how severe are your hives and itching? Are the medications that you are taking helping your symptoms? The treatment that he mentioned about suppressing your immune system is more for severe cases-chronic idiopathic urticaria and/or the problem is related to the immune system where you have autoimmune urticaria(body attacks itself) and that's when drugs like cyclosporine(usually a drug normally taken by transplant patients) may be used. But do not go into that treatment category if your problem is manageable by antihistamines. Sometimes, if the current antihistamines stop working, there are other combo(2 or more different types) that you can take.
However, if you are doing well with just the antihistamines, don't go into the immunosuppresant drugs as they can do more harm. Although the dosage is not as high as those transplant patients getting... one might be more prone to infections.
My mom has dermatographism and hers is due to infection, so after her infection is cleared, the hives no longer come back. So it might be an underlying infection or something. Hope you feel better!