Well you have ruled out a number of causes. Dry skin is the commonest cause of generalized itching. Applying a moisturizer and using only soaps that are gentle on the skin is helpful in this case. Hypothyroidism too causes dry skin. Please get your thyroid function checked. It could also be due to overuse of AC and heaters. If you have blisters at tip of fingers and dry skin then you need to rule out certain conditions such as diabetes, psoriasis, hypothyroidism, contact dermatitis, atopic dermatitis and malnutrition.
Generalized itching can be due to allergy—you may or may not have accompanying rash. Common allergens are pollen, mold, dust, pet dander, synthetic fiber, food, cosmetics (powders, soaps, shampoos—see if anything was recently changed) or drugs. Food allergies like to gluten, lactose, sea food, and alcohol etc too should be looked into. It could also be due to new soap, talcum powder, clothes etc. You must get an allergy test done, either a skin test or RAST, to know what you are allergic to. Fungal infections like tinea corporis and tinea cruris too cause whole body itching along with genital itching. Liver problems too can cause generalized itching.
If the itch is only in the exposed part, it can also be due to sun allergy. Pubic and body lice can be another cause. Worms are another cause of both anal and body itch and hence get a stool test.
In females, menopause is another reason for this. Low estrogens are supposed to be the cause. Try a diet rich in estrogens. Hormone replacement therapy can also help a few. PCOD and hormone imbalance too can be a cause. Some liver problems and gall stones too can cause generalized itch.
Since I cannot examine you and know other related conditions you may be having, nor is a detailed history possible on net, I have listed the various possibilities that should be looked into. Please consult your PCP for primary examination followed by proper referral. Take care!