He wasn't always this thin though Coff, he has always been short for his age, but not skinny. He started to drop weight at the end of year 2, so around 6/7 years old and it got much worse when he started the Juniors, so 7/8. That was when the Paed decided to test for Coeliacs, but the test was messed up by him having a D&V bug the week before, so he didn't eat any gluten for 10 days. The test was negative, but the Paed said to treat him as if he has Coeliacs, based on his food and digestive diary, as there was a clear correlation between symptoms and gluten intake. (Of course this means no dx and therefore no prescription for gf food.)
He suddenly grew and gained weight consistently for about 6 months after he went gf, but then he started having regular diarrhoea episodes again and his weight plummeted. He lost half a stone from September to January and the GP referred him back to the Paed. Paed didn't do much, other than one stool sample, when ds was well and passing normal stools - so that came back as normal. All the Paed has said is that ds doesn't seem to be able to break down fats normally, but his stool sample tested negative for pathogens and normal for enzymes.
He has had bloods taken, which came back very odd, but were overlooked initally. The Paed said he wasn't concerned about them. He is veggie and gf (so no meat or fortified cereal products) yet bloods were high in B12. They were also high in eosinophils (indicating allergic inflammation) and blood proteins. Basically he has gained and lost the same few pounds over and over across the last two years, but the Paed is unconcerned. Didn't help that their scales and measure both went out of calibration time before last and they didn't notice, so he was shorter and weighed significantly less at his last appointment than at the previous one - which was again ignored by the paed.

As a baby he was always on the 25th centile for height and in the middle of 9th and 25th for weight. His weight dropped to just above the 9th centile when he started to walk and stayed there until he got Scarlett Fever twice in quick succession in Reception year, when it dropped below the 2nd. He gradually gained up to between the 5th and 9th centile over the next year or so, then got Scarlett Fever again in Year 3, which by coincidence - or not - is when his weight plummetted again.
Over the summer we have had a couple of episodes of him screaming in pain with cramps and being unable to leave the toilet for between 24 and 36 hours. We haven't a clue whether this was because he was glutened or if there was something else going on.
There's definitely something not right, but I can't get anyone to listen or take it seriously. Paed just says that because he's dropped that low before and recovered it's not a problem. 