Not sure if it's already been mentioned, but animals often like a bit of ivy when their digestion is under the weather. (Yes, it's toxic, but they seem to know when they need a little bit of it, and it does seem to help then. So don't force it, of course.)
On greenstuff he could have in the absence of grass, a few things you might be able to try. Cleavers (sticky willy) is growing here now, that's usually very tasty for them.
Alexanders ditto. Any twigs with leaves on (that aren't toxic of course), eg., hawthorn, willow (he might like the willow bark too, it contains aspirin.) And grass replacements eg., soaked grass pellets (Dengie do them, amongst others), meadow chaff or bagged meadow grass (again, Dengie do these, as do others; mainly aimed at horses but - unless they have copper added - should be fine for sheep), even a haylage (Equine-H Meadow Haylage is very palatable and nutritious)
I'm sure we are all empathising with you right now, I certainly am.
He's fighting to live so if you're able to get enough into him and there is still hope, you feel you want to keep trying for him. Equally, he's miserable and you know you could end that. A regular dilemma for anyone with animals.

between the meds and the drenches, and maybe some ivy if he wants that, he will turn a corner very soon - and maybe find he likes digestive biscuits, as an easy way to get proper food into him, and/or you'll find a forage that tempts him. But if you feel that hope has waned and he's better off put out of his misery... Trust your own judgement, you will know when it's kinder to let him go
