Some babies dont tolerate the thickner well I would find another paed for sure he sounds very uncaring. I'm in Vic so can't help there but may post about paed on sunshine coast I'm sure other mums will be able to help. Ash had a barium swallow when he was two months so should be ok at four months. It sounds like u guys need to see a neurologist they are really good at explaining everything including MRIs we are having our 3rd later this year. If bubs isnt aspirating I'd say the feeding issues are related to reflux and similar to my ash not learning about hunger and missing out on learning to feed in the beginning due to the ECMO and other medical issues. Really feel for u, feel free to pm me if u have any other questions and I might be able to help.