Tobyluv gives you excellent advice, just want to second that. And LBJ of course.
You need to eat something yourself first of all, your brain can’t work properly without fuel. So eat something, anything really, or it will be much more difficult for you to help your bunny. And your bunny needs you to be strong and cool-headed now.
As Tobyluv says:
It is dangerous when a bunny doesn’t eat. So he must eat. By syringe if you have to. Insert syringe beteen his front teeth and back teeth, there’s a wide gap there. Make sure he swallows , don’t push too much food in at one one time.Make sure he sits up when you syringe him anything – in your lap or on a table, just put him on his back. It’s traumatic for buns and it makes it harder to swallow.
Fluids are important. Again, you can syringe water. Young animals get dehydrated fast. Did he get any subcutaneous fluids at the vet?
Pain-relief is also important. Teeth-chattering means pain. Pain aggravates any condition. If you have a pain-killer for him (metacam), it will lower his body temp as well as take away pain. So keep him warm, wrapped in a blankie or in your knee with a blankie on him or if you have a hot water bottle he can have in his cage (but he must have space enough to move away from the heat-source if it gets too hot.)Sick buns are prone to get too low body-temp, which is dangerous.
This condition is serious since he’s so young, I’m guessing he has a parasite or bad bacteria, (coccidia, or bacterial enteritis) and definitely needs proper treatment. A bunny that gets proper treatment can be fine within days. Sending so many healing-vibes for him. Please keep us updated.