Hello~It sounds like it could be Cholinergic urticaria, also known as Hives. There are many forms of Urticaria and erythema, which is superficial reddening of the skin, usually in patches, as a result of injury or irritation causing dilatation of the blood capillaries but they all cause the pins, heat, PAIN. In most people it is the histamines in there body attacking a chemical in or around the sweat glands, that's why we only notice it in times that we may sweat or release other chemical response, like excitement, stress, laughter.
I would see either a dermatologist or even a neurologist, either one should be able to help and give you the tests needed to determine the exact cause.
I hope you feel better soon.