1 month old doesn’t want to eat.

My baby usually drinks between 4-5oz every feed. The last 2 days I’ve been lucky if I can get him to take 2-2.5 oz a feed, and just that little bit takes him up to an hour to drink. He’ll drink so much and then he starts to try and spit the bottle out. He doesn’t even show any signs of being hungry. I did recently change his formula, But he hasn’t had an issue drinking it until the last 2 days.. He doesn’t have a fever or any other signs of him not feeling well. Could a growth spurt cause him to not want to eat as much? I’m afraid he may get dehydrated or his sugars drop. I will be making a drs appointment if things don’t change.