What Causes Rashes On The Back Of Hands Radiating All Over The Body?

Hi I have a rash that started on the back of my hands and spread to my arms. It has caused me to itch and has now spread over my entire body. It is very prominent on the back of my hands and arms and on the left side of my stomach. I have scratched the other side of my stomach to see if it would spread but didn t. I recently got a tattoo on my leg and thought it was infected as I had the same rash about a month ago. After seeking treatment I was prescribed prednisone, diphenhydramine, and cephalexin and stated to have contact dermatitis. The rash began as a lesion between my middle and ring finger and spread to the backs of my hands then everywhere. I have hpv and cyn2 and have had issues with rashes previously. I have a lesion on the inside of my thigh as well. The rash on the back of my hand only smells like fish really bad. I first came into contact with this rash when cleaning out my fish tank after a fish died. I think some of the water may have gotten in a cut in my hand or something. I feel very uncomfortable and would appreciate any help you can offer. Thank you.