What Causes Rash Over Neck And Chest With Itching On Body?

I've been on citalopram for 4 weeks and about a week ago started feeling really itchy. Its now progressed and I have a horrendous rash all over my neck, chest, stomach and bikini line. It feels like sunburn and looks really bad, I have a doc appointment for monday but thats 2 days away. Should I calm down and wait until monday or not and is this a normal reaction?