Itching is a symptom.
In order to be properly diagnosed you will need to be examined by your Dr and have some medical testing performed.
Some things you should think about are:
Have you changed anything?
Skin lotion, fabric softner,
Soap you wash your body with??
Any new medications?
Even old ones can be at fault
Certain medications send up red flags if you are on them and develop such symptoms(Call your Pharmacist and ask for a review of your meds and ask if there are any that frequently cause such problems.
Have you tried any new products or foods??
Have you had seafood, nuts, or foods you have had a problem with previously
Have you had any potential exposure to contagious skin disorders?
Slept over at a friends or in a hotel.
Worn anothers clothing,
Exposed areas of the skin will flare first usually in these types of things.
Scabies, ringworm, poison ivy/oak/sumac, fleas, bedbugs.
Some will cause a rash like effect when scratched..
If you always get hives with the itching , keep a food / topical / laundry product diary to see if you can track down the offending agent.
Note whether you notice swelling of the face, eyes, tongue, throat, airway, hands, legs, itching of the roof of your mouth....Do you have shortness of breath, wheezing, or trouble breathing?
There are some interal medicine problems that can cause such things as you describe as well.
I urge you to see your Dr and be prepared to answer similar questions to what you just read.
Best of luck!