advice for sleep

Hi! My LO has been waking between 3.30-4.30am recently, after his middle of the night feed. We have tried different sleeping time and it seems that once he has his 9hrs of sleep, he doesn't want to go back to bed. It's so exhausting trying to put him back to bed and he'll only go back to sleep after 1.5-2h later. I dunno if it's sleep regression... Any advice on how to let him sleep longer? TIA!