3 month old baby, stops drinking after about 70-90ml after every feed

Please help a lost mama here. My LO is 3 month old, he will stop sucking his milk after about 70-90ml and cries. We will then burp him. He is all smiley when in the burping position but when the bottle is re-offered to him, he cries and struggle. He is only drinking about 100ml per feed, every 3-4hourly I have tried upsizing his nipple teat size, trying a new bottle, but this issue is persisting and has been persisting for about 2 weeks. What is happening to my baby here :(( Did he develop some sort of unsuitability to his formula milk suddenly? Do I need to try a new formula?? Please help a lost mum here