Baby not sleeping

Recently my son hasn't been sleeping throughout the night anymore. He is 4 months old and use to sleep from 9pm-7am. I've tried taking him a nice warm bath before bed with the lavender soap and then a massage with lotion too before I feed him to go to bed. Idk what else to do. Could I get any suggestions on getting him to sleep throughout the night again . Would sleepy time tea or something like that help?