T. are you on a leave of absence with your baby or have you returned to full time student life?
Not one of our children is alike. One will sleep until you have to wake her to see if she is still living another must be fed on a timely basis. One child wakens all night long. The other child was a sound sleeper at an early age.
All through the night for a four month old is usually four to five hours.
If he can tolerate it wake your new baby shortly before he goes to bed and feed him until he wants no more. Then he won't awaken from hunger.
You can buy a co-extention sleeper that attaches to your bed and keep the baby in it so he has the comfort of your presence. That will make him sleep better.