developed this rash...

Maggie • 25🌞Mommy to💙Luca 12/31/13💙 Logan 02/14/17💙
(Sorry if this photo exposes too much ahead of time)
I've been really itchy all day. It started on my breasts and I figured it was them growing/milk ducts forming, the usual lol. Well I was getting ready for a shower tonight and noticed I'm covered in what looks like a rash... no new soap, detergent, lotion, perfume etc. 
Since it's the weekend I can't see my doctor until next week... hydrocortisone cream and Benadryl? If it gets worse is it ER worthy for relief or are those fine to use/take?
It's on my belly and chest mainly. Some toward my back.