Reflux in a 6 week old

hello,
we are looking into giving our baby Nat Phos 6x.
we do all the reflux things (keep him up straight while feeding, hold him up for 30 mins after a feeding, burp him frequently, slow flow nipples, smaller feeds more consistently) we went to a GI doctor and they gave us Famotide and i was too scared to give it to him but decided to start with one dose today. his reflux is really bad. when he was 3wks old he started declining in weight and couldn’t keep any food down. we switched to elecare formula as per a doctor recommendation and his reflux is still really bad. we’ve tried baby rice and baby oatmeal but we stopped using it since it seemed to not help and just constipated him. i decided to finally give him .5ml of Famotide today since he has only ate twice. he won’t stop crying through his feeding and earlier today after one feeding, he spit up what seemed like yellow bile. every time he has reflux, he arches his back, chokes up and coughs. he went from spitting up all of his formula at the beginning to now just having clear liquid come up. he gets so congested afterwards and no matter how long we hold him up for, he immediately wakes up as soon as we lay him down to sleep. he also coughs in his sleep sometimes from the congestion. i’ve been doing some research and want to give him Nat Phos 6x since it seems to be the only thing i’ve seen that’s helped most babies 100% of the time. every doctor we see just says he’ll outgrow it and it’s ok but his reflux is bad and he won’t calm down sometimes. has anyone tried Nat Phos 6x? what dosage should i start with? is it safe to have him take it? how long should he take it for? please i’m desperate to help him