A variant of urticaria is known as aquagenic urticaria. it can also happen with hot water specifically. Try taking a shower with cold water and see if the similar problem still exists. Without examination of the skin condition and knowing the extent of involvement.. along with this more information on ongoing medication or previous history of skin illness it is not possible to comment on the treatment that would suit you best. Please get the problem checked thoroughly by visiting a qualified dermatologist. Hope this is helpful.