I’ve had this problem for years now, I haven´t solved it perfectly but some tips have been useful. I somewhere read, and I promise I will quote the original source, some possible solutions for an allergy type of rash including trying other infusion sets for your pump. I guess you’ve already tried Skin Prep or IV3000 as a dressing. @Mila2 gave me some good advice for this.
There´s been lots of discussion about this, you might want to take a look here