Baby struggling while drinking milk

Hi everyone! My LO is 11 weeks now and has been rejecting feeding this past 2 days. We are exclusively bottle feeding and she is still using the 0+ mth teat cause she chokes easily. Tried to change to a bigger teat and she is still struggling and even choking on the milk. Sometimes also don’t wanna sit down while burping. Prior to this, she has been drinking very well, finishing the bottle. What should we do?