“Unrelenting hives?”

I was recently prescribed Diclufenic topical gel for pain due to an accident. I have always suspected I was allergic to NSAIDs from a three-day episode of full body hives after taking Advil. This was 20 years ago. Because of a shattered pelvis, I was supplementing with Aleve and an occasional Advil. This time around I tolerated it well for a few weeks but slowly starting with my hands I started getting hives. I immediately ceased the gel and talking any NSAIDs but it has been 6 weeks and I am still breaking out in hives. The Dr’s I’ve talked to have prescribed several rounds of prednisone and it abates but has not taken it away. Meanwhile, I did not do well on the steroids. I have type 1 diabetes for over 32 years and it has wreaked havoc on my arteries. The steroids made me feel like my heart was pounding out of my chest and that landed me in the hospital. The stents I got 10 yrs have deteriorated and I am due for open-heart surgery in the coming weeks. All this and still getting hives. My question is how long does it take when you have an autoimmune response to a medication? I cannot find any solution and have asked my dr for a referral to an allergist. Do you have any suggestions or any insight as to what I can do/use?