Most 3 month old babies sleep around 13 to 14 hours per night.
Also 3 month old babies are usually in bed and asleep at 9:00 PM to 9:30 PM but some 3 month old babies go to bed earlier as in 8:00 PM.
The 3 month old may also wake up in the middle of the night needing a feeding and they may not sleep fully through the night until around 6 months of age.
So be prepared to lose sleep with your baby for at least the first 6 months of the babies life.
It may seem like it won't get better but it does get better and easier on you as the parent as the baby gets older.
So just hang in there.