What you are experiencing is normal. I had the same problem as you.
As babies get bigger and their tummies can hold more milk hence their feeding hours stretches.
Do you feel engored in the mid of the night?If you do, suggest you pump out the milk.
I try to let baby sleep throughout the day so that my sleep is not disrupted. I will wake up earlier to pump and leave for work. Having enough rest helps in producing more milk.
Chen Shihan