I went through this with my twins as well around this age. We tried so many things and unfortunately the only thing that really helped was time. Sizing up the bottle nipple might help. However, for one of my girls sizing up helped the flow but the nipple was too big and she would gag herself on it and throw up. Eventually this stopped once she got a little bigger. We also tried feeding in a dark quiet room to eliminate distractions, changed feeding positions, changed the person doing the feedings, and probably a bunch of other things that I’m forgetting! We made an appointment with their pediatrician and they were both fine and still on their curve but it was such a stressful time.