Since his stomach is so big, start him on epsom salt asap.1 tsp/gal and work up to 2 tsp/gal with 100% daily changes. Do not feed him for at least 2 days.
Is he still pooping or has he not gone in a bit?
The epsom salt should help him poop within a few hours at the quickest or within the next 24 hours. keep a close eye on his poop for any abnormalities. Stringy and white is not something you want to see at all.
Are his scales raised up at all around his middle section? Is his stomach looking grey or just a bit brighter than his normal coloring?
Make sure to raise his temp to about 80 degrees over the course of a few days too. This will help speed up digestion and thus help with any constipation.