Woke up with first ever hives rash, no idea why, its widespread and very itchy, took allergy tablets but not worked, what else can i do?

See your doctor: It could be a sign of something else medically going on. If urticaria or hives the itching can e treated with antihistamines.

Hives...: In addition to over the counter antihistamines, which you should go ahead and take at the max dosage recommended on the bottle, you can also try a topical steroid cream (like cortisone), avoiding your face, armpits and groin. You also want to avoid getting hot & sweaty, as well as hot baths/showers. If you don't get relief soon, you may need to be seen for a prescription medicine like prednisone.