We switched to size 2 when my little boy was 8 weeks old as it took too long to finish a bottle plus he was swallowing more air in than normal due to the struggle of sucking the milk out. It took around a week for him to get used to the faster flow but now he is fine. Have you tried pace feeding when you keep him a bit sitting up?
My baby switch to size 2 teats at 3 months. 2 months was far too early for her as she kept choking. She is now 6 months and on teat 3. Try not to hold the bottle up so high and keep the milk in the bottle level with your baby’s mouth. It will slow down the flow slightly. I found this really helped. Maybe burp him half way through the bottle too. Hope this helps xx
My LB went on size 2 test at 2 weeks because he’s a big baby and was falling asleep or just not finishing a bottle and was then starving 30 mins later. My health visitor said as long as he’s not choking like it’s coming out to fast it’s fine. My LB didn’t and took to it fine x