Well, if it's a herx - then it means it's killing the nasties...but if it's an allergy - that's not so good.
I re-read your first post - that is really quick for a rash from herxing....
I would advise you to add in some more detoxing methods, and keep an eye on it...if it gets better with effective detoxing, then you know it's a herx.
Epsom salt baths are a great one...and if that's not possible, you can do foot baths.
Alka Seltzer Gold is another popular detox.
Also, are you taking good probiotics? - Daily? Even though you are on IV and the abx aren't in your stomach, you still need to take the probiotics daily.
You could add some fresh squeezed lemon to some of your glasses of water. But, you might want to drink with a straw, so not to damage the enamel on your teeth.
There are more detoxing ideas here:
www.tiredoflyme.com/detox-methods.html