HELP 😬

I am a frazzled, overtired ftm who needs help. I have an almost 9 week old baby who won't sleep! All day today, he's been up a lot today so I thought he would sleep great tonight. Not the case. I put him to bed at 8:45 and he slept until 11 which was fantastic! He went right back to bed after eating but then was up at 12. I thought "alright, I'll feed him and he'll go back to sleep!" Nope. He's been up partying since then and it's almost 2 in the morning 😑 I haven't slept at all. I know he's gonna start getting overtired but it's like there's nothing I can do. He just keeps talking and smiling at me and I'm so frustrated and I love his little smiles but his talking is waking up my fiancé who has to work. I feel like he's getting his days and nights mixed up. What can I do? Help!!!!