My baby is taking significantly less milk than before. Should I change the formula?

Hello doctor,

My son is 14 weeks old. His weight is 15.4 pounds and length is 2.1 feet. He is formula fed since birth. I noticed that in the last month he began to take significantly less milk than before and I cannot understand why. Between 1 to 2 months of age, he used to drink around four cups per day. However, between 2 to 3 months of age, he went from four cups to around 3.5 cups. He seems agitated when he drinks, flails legs and arms; sometimes he will not suck well and just bite. Then, he will drink around 3 to 4 fluid ounces and rejects the bottle, but he will continue to suck on his hands and moan. He will grimace at the bottle and even vomit if I insist on giving the bottle.

His bowel movements are regular to around once or twice a day, yellow and soft. Sometimes, he has a bit of reflux after eating (some milk coming out), but less than before. How to fix this problem? Am I doing anything wrong? Should I change the formula?

He has gained 2.2 pounds in the last one month, but I am concerned that he seems to drink less milk as the daily quantity keeps going down. He drinks around six times per day around half a cup each time.

Hi again Dr, I'm writing with the same problem that seems to have gotten worse. In the last 12 hours my baby only had only 3.5 fluid ounces (3 fluid ounces at 4am, then 0.5 fluid ounce at 8am). Last time he had 0.5 fluid ounce, then stopped and sucked his hands for 1 hour and is now sleeping. Didn't cry at any point. He keeps sucking his hands but will not take the bottle or just take it for 1 to 2 minutes and then stop. He seems alert and happy, almost agitated. He gets really agitated when he eats. Is this still nothing to worry about?