Hmmmm... I am thinking there might be a clue in the last sentence. Do you think your older son might be wanting to be in the bedroom with you and the new baby (if he's there), or wanting extra attention because of the competition?
You might think of ways to include him during the day, let him snuggle up when you nurse your younger one(if you do), etc... and get some special time with him, without the baby, and maybe some special privileges that might be contingent on his staying in his room and not waking you up at night? Try being firm, telling him that you need sleep and he is not to wake you up.
Or some might say, put a mattress in your room for a while and let him sleep on it, ONLY if he's willing to be quiet. He may find he doesn't like being roused by his baby brother, and will appreciate sleeping in the other room.
Is there a Dad or partner who can help? Whatever you do, try not to inadvertently reward him for getting up in the middle of the night.... have the other parent put him back to bed.
At bedtime, a nice routine, reading and singing to him, might settle him. But NOT to be repeated in the middle of the night.Read him A Baby Sister For Frances and other books about the new baby coming and the older sib's feelings.
The Family Bed people would say just take them all in your bed. That works for some, but never worked for us!
Good luck.