Failure to thrive - digestive issues or allergies?

[SunshineLollipops9]

DS is 10 months old and faltered growth/FTT (0.4th percentile). He has multiple allergies- Dairy, soy and wheat are FPIES and egg & peanut are possibly IGE waiting for skin pricks.

He had a slow start to weaning, which we think was possible because of all the allergic reactions he had. He is getting better now but still not much appetite. I have been trying to add bigger portions and higher calorie foods. He seems to be pooping as soon as he’s eaten and has awful sounds coming from his stomach with some undigested food. So I do wonder if that’s normal weaning poo or he’s struggling to digest which could also cause the growth issues. He is under paeds and they weren’t concerned last time they saw him as he was happy but now he hasn’t grown in length since the end of Jan.

If you’ve had this before I’d love to know if it resolved for your little ones or what it turned out to be?

No advice but 7month old LO also struggling to gain weight (91st to 19th percentile & continuously dropping as weight gain is pretty much nonexistent). Not terribly concerned but LO just has no interest in feeding or milk. Would rather grin at me than swallow anything! No allergies that we know of, just would rather play than feed. Not as severe as your situation but thought I’d send a hug because it’s so stressful <3

My DS was considered ftt at a year old. He was put on fat supplements to increase his calorie intake. At one point they thought he had cystic fibrosis. Multiple tests and they didn't come up with anything other than watch and wait. He was always low weight but otherwise healthy apparently, except for multiple allergies and asthma.
A number of years later he was diagnosed with a connective tissue disorder - which can affect digestion and many other complexities. I am still cross that not one of the many medics we saw over the years even thought about this as an option. It would have saved my ds a lot of pain and injury if we had known sooner and had proper support. I have sadly heard many similar stories since.