Not eating well

Mystery

My baby is 12 weeks old. 6 weeks adjusted. He went from eating really well, like 4 oz every 4 hours, to eating like 2 every 3-4 hours. He eats pretty good during the night. Like 3 oz every 3-5 hours. He gags a lot when I try to put the bottle in his mouth and most times won’t eat. He will only eat if he’s like really hungry. Is this normal? Or should I call?