If you have tried the 3 doses of infant gas drops and your bun doesn't seem to be improving by now, I would suggest getting him to the vet. There they can rule out bloat or a blockage, and can administer fluids, pain meds, and gut stimulant, and send home extra meds and feeding mix for later.
If he does seem to be improving, I would try to offer some of his usual leafy greens. Those seem to be the first foods my rabbits will eat after feeling sick.
If he does seem to be improving, I would try to offer some of his usual leafy greens. Those seem to be the first foods my rabbits will eat after feeling sick.