One of the common cause of generalized itching is due to Scabies. Please read the symptoms of scabies;
Scabies do not have over the counter medication, so a prescription is needed from a doctor for the treatment.
Meanwhile you can apply calamine lotion, which can help in relieving the itching.
Following would help you;
1) Avoid exposure to heat and humidity.
2) Use moisturizer, if you feel that your skin is dry.
3) You can also try skin-soothing oatmeal or cornstarch bath for itching.
4) Wear cool, light, loose bedclothes. Do not wear rough clothing, particularly wool.
The other causes of itching are, if the scabies is ruled out;
1) Dry skin; happens in winter months; baby Johnson oil or any moisturizer would help.
2) Skin allergy
3) Kidney, liver disease (than it is termed as pruritus); investigations would be needed to ascertain it. Please read the causes of itching in this authentic resource;
Following investigations are usually advised;
a) Complete blood counts
b) Total eosinophil count
c) Vacuolated eosinophil count
d) Liver functions tests especially serum bilirubin
e) kidney function tests (blood urea and serum creatinine).
If you have a family history of diabetes; that should also be ruled out for your symptoms.
Please feel free for your follow up questions.
I would be happy to assist you further, if you need any more information.