4 month old crying before EVERY nap

Alli

To start, she does have CMPA (cows milk allergy) so I am on a strict no dairy or soy diet. She was doing great for 2 1/2 weeks and then all of a sudden the past 9 days is SCREAM crying before every single nap. Like screeching for 10-50 mins each time. I don’t know if anyone has been through this, maybe part of sleep regression? Teething? Gas?