not sleeping through the night anymore

I feed my baby around 10 pm and put him to bed, he's ebf. He used to sleep until 5 or 6 am, well this is my second week back at work and then he moved from waking up at 5 am to 4 am and now he's waking up to eAt the last few days at 2 and 3 am! The bedtime routine is the same as its been. It's very frustrating and very tiring for me. Anyone experienced this? Any advice to get him to sleep longer? He sleeps in my room next to my bed .