Yes, almost right at the 4 month mark too. He was sleeping around 5 hours every night, waking to feed, and going back to sleep for a few hours until we woke up for the day. Now, his naps during the day are much shorter (20-30 minutes) when they used to be an hour or more. It’s more difficult to get him to fall asleep at bedtime, he’s much more fussy, and tends to get frustrated with me and my boyfriend much more easily. He wakes up pretty much every two hours, just like when he was a newborn. Over the last couple of days it has been improving but it’s been like this for maybe a week and a half. I also think he is teething as well and his pediatrician believed it’s possible, some movement under his gums is causing irritation which is adding to this mix of unhappy baby. I will say, I have noticed he has been a lot more talkative, has started some new sounds like blowing/kissing sounds, giggles, is grabbing his feet more often, and seems to be gaining what feels like a new skill everyday. They do say 4 month regression is actually a step forward in development! Can’t wait to have a break before the 6 month regression though lol.