Our LO did this from about 3.5 months to 4.5 months - he no longer fights naps but his nighttime sleep is horrible, and it’s been 1.5 months of no sleep for me. My husband helps but because I nurse, I end up doing most of the night care as well. He has gone from waking every hour or two to now three hours (some nights) which has been great so it’s better not great. We figured out his wake windows were off and started using weebeedreaming on Instagram’s 5 month old schedule, and he’s been easier to put down for naps and bedtime. The four month regression is absolutely brutal and I’m sorry you’re going through it. Is it possible for you to get some help during the day so you can squeeze in some naps? That’s what I had to do - my mom and MIL came over and would watch LO, so I could sleep.