Quick trip symptoms and conditions

I used Cystex for the symptoms of a UTI, within two hours I had a horrible raised facial rash that was burning horribly and spreading rapidly. A quick trip to the ER, some prescription strength steroids and antihistamines quickly reversed the side effects. One day later I still have a residual dry itchy rash that is significantly smaller than before the ER, but hopefully with the continued medications I received I will be 100% better soon. By the way I did have a UTI and was prescribed something for that too, so it was not a totally wasted trip, just a bit more dramatic than usual. I have been advised to avoid Cystex or any product that has any of the same ingredients from now on. The next allergic reaction might be more severe.
Female 38yo - Texas