Help please. 2 1/2 year old son and sleeping

So my son has had his one room for about 4 months now. He got his own room when my daughter was born. Ever since he got his room he wakes up in the middle of the night crying. This happens pretty much EVERY SINGLE NIGHT. It’s always usually from 1-3 am anytime between that time. He wakes up crying and we go and put him back to sleep but then he wakes up again and comes to my room crying so much that I let him sleep with me. It’s been a big issue because I have my 3 month old daughter and it’s so hard to have both of them in the same room sleeping because he wakes her and vice versa. Idk what to do. I try to get him to sleep early because he will not nap during the day anymore. But has anyone had this type of issue. 😩😩😩😩😩