Your baby may pee a lot at night because they have drank too much liquids before bedtime.
Or just because they are hydrated enough which is good.
It's normal for babies to pee a lot during the night and during the day as babies bladders are small and they also have no control over their bladders.
As a babies bladder fills up they release the pee into the diaper without realizing it and without being able to hold it back.
This is a reason we make babies wear diapers because babies pee constantly and would pee all over their clothes, floor, us etc without a diaper.
As the baby gets older the baby will usually begin holding their pee in for a bit and then release it.
After a year old the baby will usually be able to hold their pee some and then pee every 30 minutes to an hour and as they get to 2 years old and above they can sometimes go a few hours without having to pee and without having a wet diaper.
Be sure to change your babies diaper before bed and if the baby pees a lot you may need to change the diaper in the middle of the night before he or she soaks through the diaper.
Also consider using overnight diapers or double diaper the baby by cutting holes in the first diaper and then putting another diaper over the first diaper to increase absorbency.