I’m beyond frustrated. I need help. I want to sleep!!

I have semi sleep trained my kid he’s one 18 months this month to be exact. Semi trained meaning he can fall asleep by himself. He has a milk and I lay him down and he falls asleep almost immediately. Now , during the day he sleeps like an angel. But at the night he’s constantly waking up! Multiple times a night , yes I wear him out he goes to the park and walks for awhile or whatever it is we’re doing that day. When it’s time for bed , I brush his teeth, he takes a bath, gets into his pjs, drinks milk and then goes to sleep. Which is great but let’s say he goes down at 7:30pm ( he wakes up early like at 6:30am so it works for us) he will be awake crying at 10:50/11pm like what am I doing wrong ???!!! From there on it’s constant waking up constant crying and whining. Like does he know how to self soothe or not? He sleeps in a bed next to mine so his own space btw. I just need help on what I can do.. I start a new job soon and I’m so sleep deprived..