ANSWER:

No problem. 

However, Prophet salla Allahu alaihi wa sallam prescribed us to pray witr as the last prayer of the night but if you happen to stay up late after offering witr and wish to pray night prayers later on or if you got up after praying witr (after isha) and wish to pray night prayers then no problem in that. 

QUESTION: Can i perform other nafls after witr?

Prayer, Taraweeh, Tahajjud and Qiyam-ul-Layl |