I've had this itch for like 9 weeks now. At first it would just be blanched hives which would last a few hours. They would appear all over my body. I was diagnosed with atopic dermatitis, was told to avoid common allergens and was prescribed two antihistamines as well as a corticosoid cream. They partly relieved my itch but it still went on. Now after I've stopped them because my dermatologist said so they are very bad again. This time the hives appear like mosquito bites (despite me not having any contact with insects FOR SURE). Around them I also get clusters of very small bruises (which are probably broken blood vessels). It's been incredibly unbearable and for now my dermatologist hasn't been able to help.
In addition to your dermatologist, you probably need to see another type doctor to do additional tests. Make sure you get an allergy test and I hope the dermatologist took a biopsy. Best wishes for you!