He has GI stasis and if the right things aren't done he could very well die. He could still die no matter what you do, that's how serious this is, so he really needs to go to the vet.
Aside from that, you could try the simethicone infant gas relief. At that age I'm not sure what would or would not be good. For an adult the dose is 1cc every hour for 3 hours and then 1cc every 3-8 hours after that as needed. So with a baby, if it's even safe, the dose would have to be a lot less. Pain meds would help too, but you have to get metacam from the vet, and I don't know what they do for a baby bunny. Baby aspirin can be used for adult rabbits, but I don't know about baby rabbits, and I don't know the dosing. The simethicone is to help with gas bubbles but that isn't going to solve the problem. There's a slowdown and blockage in the digestive system. A complete blockage requires surgery. If it isn't a complete blockage, then GI motility drugs can help, but those also come from the vet. The most important thing is the pain relief so the rabbit will want to start eating again, and to get liquids and food into the digestive system to aid in moistening up the blockage and get the GI system moving again. Oxbow Critical Care is a food mix for sick rabbits. The vet has it and some stores online have it. You can try and use a moistened pellet slurry. You will need a large syringe to try and syringe feed your rabbit with, you also need to give water. The water and fiber from the food is very important. You need to be careful syringe feeding and do it slowly so that especially the water, isn't aspirated. With adult rabbits you can try giving leafy greens like green leaf lettuce and cilantro, but baby bunnies are more senstive to fresh veggies, so I don't know, but with it already being sick, if he'll eat leafy greens on his own it might be worth a try. You need to get moisture and food into him and get him to the vet ASAP.
If he for sure is drinking, and drinking a lot, then you don't need to syringe feed water to him, but he does need the critical care or pellet slurry. I don't know how much, maybe up to 3cc every 3 hours.