How to keep him on the same schedule 🤔

So my 13 week old little guy is very happy baby he takes about 3-4 naps a day and every day is a different time we kinda work around his schedule for right now. When it comes to a nigh time you hit or miss one night he will wake

Up once sometimes twice sometimes 3-4 times I don’t understand why every day he goes to bed same time usually around 9 but then u never know when he wakes up again I know he can go through out the night with one time feeding I don’t understand why he can’t stay consistent and sometimes wakes up 4 times idk what I’m doing wrong I work full time and I wish he just stayed consistent with his night feedings but idk how to help him some days I’m so just sooo tired. Thank you mammas for any advice ❤️