To start with as you said you don t have any known allergies ,but sometimes we are unaware so taking anti allergic medications like tab Allegra 180 mg at bed time for three days , you can make sure that it s not allergic. other common reasons can be itching due to eczematous changes, or some cosmetic allergy. stop using any new things which you might have started esp like deodorants, cremes in recent past just before such episodes Check whether are you having any infections around the areas whether you are getting that sensation, if you are unable to understand, please visit a nearby doctor.Some parasitic infections like scabies, wt Nile fever are also associated with itching. medication will be provided accordingly after source is identified.do not use self prescribed ointments which can flare up the infections if not used wisely. Dust exposure, asthma, hay fever are some other conditions too other than this check whether your stool habits are fine and whether you have developed any yellowish discoloration of eyes, urine and passing any pale stools as obstructive type of jaundice or bile duct problems can manifest sometimes with severe itching. the best way to tackle would be to apply ice cubes for reducing the inflammation. Then try to figure out any allergic substances that you might have come in contact with, and take the medication as per your physician advice if you are unable to figure it out yourself.