Rash appeared after giving birth - advice needed urgently!

I had a baby boy exactly one month ago. Almost immediately after I had him I developed a rash, firstly on my stretch marks which became red, raised and itchy and then all over. It is red, very itchy and has a raised appearance with some spots that look like mosquito bites. It moves around and seems to disappear slightly only to reappear in another location. When I have a hot bath it makes it worse and the redness and itching intensifies. I scratch a lot and although I tell myself not to, it is hard not to. I have been to my doctor who said it might be an allergy or it might be herpes!!! (I don't think it is herpes as there is no way I could have got it unless the hospital was very unhygenic or something). I really don't know what to do. My doctor is useless. I have tried several creams - anthisan, calomine lotion, kamillosan etc and just wondered if anyone has experienced anything similar or can give me any advice of how to treat it. This is the last thing I need to deal with as I have a month old baby to look after and I am starting to wonder if it will ever go :(