Welcome to the forum.
I'm glad you found us, although I'm sorry you and your son have to be a part of this terrible club.
Some meds work for some and not for others.
For me, the traditional meds failed me and the mesalamines I
became intolerant of.
And when the doc gave me a choice of surgery or remicade, I
balked and had to find my own way.
He also told me diet has nothing to do with UC, but I found
that it has a great deal to do with exacerbating its
symptoms!
I found that by doing these things it helped control my
symptoms by 75%:
1) adequate high intake of vitamin d3 ( need to get your
levels checked first)
2) probiotics are key, are you on any?
3) slippery elm powder to coate the intestinal tract helped
greatly
4) l-glutamine amino acid powder for long term colonic
repair
5) food combining
6) diet modification as in gluten and dairy free
7) rectal meds help lots of folks out
Be careful with cheese, your son may be allergic or intolerant of casein ( cow dairy protein). I would suggest he stay away from all gluten and dairy for now, until things calm down a bit. Also, some of the foods you mention his having do contain hidden gluten, which he may be reacting to. I would suggest you try proteins only and see how he does for now.
Proteins are typically very easily digestible.
I started out on SCD, but eventually found I did much better on Paleo.
Slippery elm powder is a great idea, look into l-glutamine powder as well.
The Last 25% was taken care of by LDN, low dose naltrexone,
which put me in remission.
If any of this interests you, there are
things IMO that you can control, which will have a direct impact on your
disease, the symptoms you experience and their severity.
I was able to control my UC into remission through various
supplements, probiotics, diet modification, and LDN , low dose
naltrexone.
For more info on the protocol which has put me into remission,
please go to this link: https://www.healingwell.com/community/default.aspx?f=38&m=1666318 , and look at the 11th post.
I hope you feel better and let us know how we can help
you.