what is going on? 😥

My lo is about to turn 6 months. For the past couple days he wakes up screaming during his naps. So far this has only happened during the day. He falls asleep and throughout his nap he wakes up screaming a couple times and I have to rock him back to sleep. Anyone know why he does this? He's exclusively breastfed.. I don't think there could be anything bothering him in his sleep. This doesn't happen at night, only during the day.