Well, firstly hello and
Generally in order to get an idea what's wrong, we'll need more info.
When he moves, does it look like he's injured or in pain? Any limping, abnormal posture, face changing color rapidly (like going pale then normal color again suddenly?)
Are his feathers fluffed up, as in standing on end, or is he just hunching up? Completely puffing out can indicate nausea and toxicity, whereas hunching tightly more often indicates pain or being very cold (or both).
What's his poops like?
Is he breathing normally?
What's his face/comb/wattles like in terms of color... Paler than normal? Purple or darker around the edges? Mottled?
Is he eating at all? If in doubt, (this should be done anyway) check his crop first thing in the morning and see if it's emptied normally as it should have overnight. Should feel empty in the morning. You can check him right now and you'll know whether or not he's been eating. If it's very hard then it might be a crop blockage.
You may need to separate him in case any of your hens is an opportunistic bully.
Best wishes.