Thanks for your query.
You have got itching sensation over tip of the penis.This could be due to two reasons 1) You may be a diabetic .In many patients this is a presenting symptom of Diabetes
.So get your blood Sugar levels (Fasting and post Lunch) done to rule out diabetes.
2)You have noticed a collection of white material behind foreskin which is nothing but a smegma
which is normal secretion of glans Penis
.You have to clean it everyday while taking a bath.