Metacam is given once every 24 hours, so if it's been about that long since the last dose, then you're ok to give the next one. For syringing meds/food, you can burrito wrap your rabbit snuggly in a towel, you may also have to hold the back of his head/neck firmly, so he can't pull away, but still you have to do it gently so you aren't squeezing, then syringe into the side of his mouth. If it's been more than 12 hours since your rabbit last ate or drank anything, you are also going to need to syringe him food and water. If his body temp is cold, you need to warm him up first with a warm pack or warm towels, before feeding him. If you can't get any critical care from the vet right now, you can use plain canned pumpkin(no added spices) or if you can't get that you can soak pellets, blend them in the blender so it will be smooth enough to syringe feed, but only do that if you absolutely can't get the pumpkin. But try the simethicone first, and after a couple doses an hour apart, it hopefully will start helping and he'll start eating on his own. If he doesn't start eating on his own an hour after the second simethicone dose , then you are going to have to do the syringe feeding, and syringing water if he isn't drinking. Just make sure to syringe slowly and give him time to swallow, or he can breath it into his lungs, which is bad. Then tomorrow get some critcal care from your vet. Also, keep grass hay in front of him. That is going to be the best thing for him to be eating right now. Some of those veggies that the vet suggested can cause gas with some rabbits, and may have made it worse for him.