Stomach question

I need some insight. This is my 2nd baby, but first time dealing with these issues. My son is 7 weeks old and when he gets to the last oz of his bottles, he gets so gassy, fussy, and irritable, he cries after and acts like his belly hurts. He seems to want to eat more but can’t, he only has 2 oz’s every 2/3 hours. He vomits a lot sometimes 1/2 hours after bottles. I burp him regularly and keep him upright after feedings for 30mins to an hour. His dr has him on acid reflux medicine, but I’m not sure it’s doing much? I plan to talk to her about this at his 2 month appt. has anyone dealt with this? What ended up being the issue?