I am an uncircumcised male, every time i wash my genitalia, the next day it becomes incredibly itchy for the next few days. what am i doing wrong?

Get checked: not uncommon to develop a mild fungal infection due to retained smegma and perspiration. Additionqlly, use only gentle baby soap to wash if this is a recurrent issue.

Soap residue: As advised by another doctor, use unscented soap only. If washing is causing the itching, you may be allergic to one of the ingredients in the soap/wash or more likely have not washed off the soap thoroughly after washing.