Could he be copying any behavior he sees at home or anywhere else, has he an older sibling or family member that hits or yells. It would be better to take off the diaper at nights you are enabling him to wet himself let him be in control of his own body, you can put a protective sheet underneath the regular sheet in case of accidents make sure he doesnt drink too much in the evenings...bathroom before bed..Forget the word discipline , focus on his good ,positive side and praise him when you see him doing something right .