I'm surprised the MW advised a fast flowing teat but I'm no expert and definitely not on bottle feeding so maybe that's correct.
If you want to give breast milk I'd get some RL help with your latch as must be exhausting exclusively expressing. I'd do it soon so LO learns how to suckle which will also regulate your milk supply and generally make life easier
I am no expert but does he have a touch of reflux? Dd was sick after every feed (not a bit of posset, properly sick) from about 3 weeks onwards.
She also started eating more frequently- the paediatrician later told us this is common in babies with reflux as the sucking action keeps the stomach contents down so they often suck for comfort.
We did have to get some medicine for her but other things we were advised were to feed in an upright position and keep her upright for at least 20 mins after, try burping her every 2-3 mins during feeds as wind can make the problem worse (personally we found this upsetting for her as she was so eager for milk so we burped her every 5 mins or so), use slowest flowing teat as holes which are too large can make the milk flow too fast for baby and worsen things.
My baby is 3 weeks old and just got back to his birth weight, he is having expressed breast milk because he didnt latch properly. Over the past two days he has started to eat less but more frequently he is now sick after feeding. My midwife recommend trying a fast flow teat to stop the sickness. Any advice apprciated.