red itchy rash that moves around

Dear Doctor, I have a red itchy rash that sometimes looks raised and also with some blisters that move all around on my body! Arms and legs chest and everywhere. thought I was allergic to effexor xr but now I don't know what is causing the problem? I am a sixty-two year old married woman and my husband can't have sex he is 68. I am thinking the effexor but it could be something entirely different? I have been having this for a month or two. We have been married for 35 yrs and have been faithful to each other. the rash can be in one area in the morning and go kind of inactive in the afternoon but I can still see where the bumps are,it seems to be getting worse! I have an apt. with an allergist in a few days but I think I should be going to a dermatologist! Very itchy and it is hard is stand! Chiffon408