Feeding

My baby will be 12weeks on Thursday and lately he doesn't want to finish his bottles; 2 weeks ago he was up to 5oz then all of a sudden all last week and the weekend I couldn't get him to drink more than 2oz; if he took the bottle all in one take he's drink it all if he stop cuz needed to burp can't get him to drink the rest; he'd get it suck once then turn his head and push it away with his hands yet fusses cuz he wants it or something; could it be the bottle he has acid reflux so due to that I haven't moved up in nipple flow