I would just keep your vet updated on the horse's status, they should know what to do. Have someone keep an eye on him to make sure he isn't rolling or acting like he is in a lot of pain as that can cause more serious problems.
I thought my mare was colicing once, but after it went on for 3 days and the vets ran mineral oil and all that good stuff through her twice, they decided to scope her and found she had a large stomach ulcer that was causing the colic symptoms. I mention this because like your guy, she wasn't acting like she was in too much pain, just wasn't eating and looked uncomfortable. Perhaps if your vet's treatments aren't working it could be something like that...
Good luck to you, keep us updated as well!
Thanks and Gig'em!