What Does An Itchy Rash On The Chest Indicate?

I ve developed an allergic reaction...rash on chest...to benadryl. I then tried Xyzal, then Zantac & each made the itchy rash worse. I m on a steroid but the rash has spread & is getting worse. I scratch & rub...I know I shouldn t...& these tiny blister-like rash, along with deep purple color, won t go away. I ve read that there are 2 generations of antihistamines & the family of the ones I used are the older, original type. I NEED to stop this itch! I ve had this rash for 3 weeks, seen 2 GPs & a dermatologist. She has taken samples of the blisters on my back & chest & they are skin type. We are waiting for the blood test results. Please help me stop this horrible itching. I m also using lidocaine 3% & otc Aspercreme with 4%. I tried several topical RX meds & they made it worse. Please help with something that ll stop this itch. A 2nd generation antihistamine???