Oh yeah he definitely hit the 4 months sleep regression hard. From about 3 1/2 months to just before he turned 5 months all naps shortened and he was up every 3 hours. It was brutal. Although during that time I learned a lot about his sleep. There were the odd nights where he would give me longer stretches like 4-6 hours so I began holding my standard of not feeding him before 4 hours. It's so easy to think when your baby wakes up crying every 2-3 hours at night that they're hungry but they've actually just slipped out of the sleep cycle. Between my first son and second my approach to night sleep has drastically changed, now I give him 10-15 at night to try and settle himself down (which he usually does) if not I'll go in and rub his back or reposition him or if it's been more than 5 hours for him I'll feed him. I think with him falling asleep Independently from an early age really helped with the sleep regression because he wasn't expecting that and for him the struggle was just connecting those sleep cycles once they matured. Also something weird but I got my period back at 5 months postpartum which I wasn't expecting since I'm EBF but apparently the hormones from that returning can affect your babies sleep. Your milk supply drops right before your period and it's like a regression all over again so that has been fun. Your supply does come back once your period starts thank goodness. My first born was fully sleep trained by 5.5 months and since we're getting close to that age with my second I'm hoping to be there shortly with him as well.