Refusing feeds cmpa

Hi all.
Not sure where to turn with this.
My son (3 months) has suspected cmpa, symptoms included severe silent reflux, rash, wheezing and coughing when drinking, constant hiccups and dropped his intake from about 32oz to about 27oz.
He was prescribed Aptamil Pepti 1 but his feeds dropped again to about 24, but it was still a struggle to get this down him and the only symptom that improved was his rash.
He was then prescribed SMA alfamino and has been on it for about 6 weeks. He hasn’t been able to get used to the taste of this whatsoever, I’ve tried vanilla, crusha and nesquik powder (all recommendations from cmpa Facebook group) to no avail, and just persevering with no flavour. He’s been slowly reducing his feeds over the 6 weeks and really fights the bottle after 2oz. I burp him after 2oz and he either refuses to go back on the bottle or I have to syringe it in which he hates.
I don’t believe that he’s not hungry, because he was on 75th centile and loved milk at first. He hasn’t had any obvious growth spurts and increased his feeds ever, every feed is the same and the struggle is the same every bottle.
He is also on 10mg Omeprazole and carobel to thicken his milk.
The past two days have been the worst and he hasn’t taken more than 3oz a feed and I try him every 3/4 hours with a bottle. He gags on the bottle after me burping him, like he’s full to the brim. In desperation I bought some normal formula for him to drink Just to see if it was the taste, and he’s still the same!
I just can’t figure out what’s wrong. He has been a pretty unhappy baby since day 1 but seems ok in himself, just constantly chewing his fist so I know he said hungry.
He has seen a peadiatrician who prescribed the omeprozole and said to wait for a dietician referral but I don’t know where to turn now he’s just not eating much anymore. He doesn’t seem dehydrated yet but I don’t know what he should be drinking to keep hydrated enough anyway, and obviously I’m worried about possible dehydration. Sorry for the long post!