Hello
Welcome to health care magic,
I would keep a possibility of acute
urticaria or
shingles first after going through your description.
It might present as skin welts/swellings which can be seen commonly on hands and legs but it can also be distributed all over the body.
Itching is subjective in individuals which could be mild to severe.
Urticaria or allergic hives can occur due to various causes like,
Infections (bacterial, viral, fungal) or certain drugs(Pain killers/ antibiotics or certain foods and food additives/preservatives or It might be physical urticaria occurred as a result of physical touch,pressure, heat,cold,
anxiety, exertion etc.
In a few cases, no underlying cause is found and are known as idiopathic urticaria.
You can continue with oral antihistamine like
benadryl (which you are taking already) or tablet levocetrizine 10 mg twice daily for 2 or 3 days.A topical soothing lotion like
calamine would also be helpful symptomatically.
I would expect that you will start improving in 2 or 3 days and in case not,then it would be advisable to see some nearby doctor who may order routine blood counts with ESR after careful inspection this rashes and can prescribe you appropriate treatment according to the underlying cause.
Hope this will help you.
Regards,