Hi, welcome to the forum, your body rash seems secondary to allergy known as atopic dermatitis and also other strong possibility is irritant dermatitis. Remember if you have been exposed to any chemical (detergent, shampoo etc.) or new garments which might have caused irritant dermatitis. if it is present, Avoiding these situations is helpful for acute flares as well as for long-term management.
Other forms of treatment are use of anti histamines and corticosteroids against prescription will help to reduce itching of the skin as well as rash.
Before that other possibilities are needed to be ruled out. Other possibilities needed to be ruled out are viral exanthem, Mycoplasma pneumoniae - serological test and chest radiography is important to rule out and should be treated with appropriate antibiotic, Rocky Mountain spotted fever (it is tick borne disease and needs serological test for diagnosis), infectious mononucleosis, scarlet fever; as a result of streptococcal tonsillopharyngitis, Kawasaki disease, and dengue. Hence, you need to undergo serological tests for few common causes.
Yes, you need to consult dermatologist without delay. Take care and regards.
You can try some over the counter Benadryl that is for Allergies. If it is bothering you to much then maybe call your doctor and see if you can get a same day appointment.