Be kind to yourself and skip the Xifaxan, Neomycin, and Nystatin for now. They are only treating a symptom and not a cure. I did herbal treatments two times and the effect lasted for 1 week each time.
That set me on the path to trying the low FODMAP diet and carbohydrate restriction. Look up Dr. Norm Robillard's Fast Track Diet, it restricts carbs that ferment readily like pasta, rice flour, juices, some fruit, and of course cakes/cookies.
https://digestivehealthinstitute.org/fast-tract-diet/
The fast track diet uses a point system to rate foods and portions of those foods, sometimes you can eat a highly fermentable food if you keep the portion small. There is a really low cost app for both the Monash university FODMAP diet as well as the Fast Track diet which I find really helpful.

If you do the work you will discover what is causing your digestive issues. After completing the FODMAP elimination diet I found I was sensitive to fructose and fructans at amounts that should be safe under the FODMAP diet, honey is a big no-no for me. When I get a hint of acid reflux (the first sign of SIBO for me) I cut back on carbs and try to figure out what food I ate too much of in the past 3 days.
Hopefully when you find the foods that are upsetting your digestion your rashes will go away. I had a knee rash since early childhood which went away when I gave up gluten. If you have a tendency towards psoriasis peppers and potatoes can cause a rash. This may sound stupid, but if you have sensitive skin be careful with how much laundry detergent you use and skip the fabric softeners. I was getting a rash and it was from my laundry detergent so I cut the amount I use and it went away.
Link to Norm Robillard and histamines on YouTube

You can schedule a phone appointment with Dr Robillard and talk through your issues. I had tried the Fast Track diet and kept my fermentation low in the low 20's for over a week. My symptoms should have resolved, he told me "Something else is going on". He was right, I did the FODMAP elimination diet and found the fructose/fructan sensitivity issue.

Hope something I shared helps!