I am using Dr Brown's bottles as well. You can try Level 2 nipples if you think you baby is sucking very hard. If your baby suck too hard, he/she will swallow a lot of "air" inside the stomach and may make him/her easy to 嘔奶.
Joyce
祝善謙氣宇軒昂、俊逸不凡!
善良忠實氣宇軒,
謙遜有禮俊逸顯。
Thanks to Joycelyn for such a nice poem!