5 week old now wakes every 45 min

Hey! So my baby used to sleep great 1.5-3 hr stretches but now he consistently wakes up every 45 min! We used to have an overtired problem but we've worked on that and now we put him to sleep when he is showings signs of being tired, and he falls asleep pretty easily if we rock him and such but then he's up after 45 min. Regardless of being held or not. It's getting annoying because we can't get any sleep! Any tips or anyone know why he is now regressing?