What Causes Tiny Blister Like Red Rashes On Arms Leading To Itchiness?

I have a rash that started out as a few tiny blister looking on my lower part of arm, turned red & itchy & has moved up my arm... what could it be... I also have a cough & other symptoms & didn t know if the rash could be related... the rash seems to have showed up first... rash started about a week ago, cough started about a couple of days ago... I also had a out patient surgery yesterday to remove to small mass from each breast... I now have small sores/blisters on my tongue... not sure if its from the anaesthesia from surgery or from whatever illness I may have...