If you haven't been syringe feeding regularly every 4-6 hours, I would start that immediately. It's not good for a rabbit to eat little to no food for more than 12-24 hours, or it becomes an emergency. If you feed your rabbit a hay based food pellet, that can be soaked in some warm water and made into a mush, then using some sort of large tip feeding syringe (so it doesn't clog) to feed with, or other method to carefully and slowly squirt into the side of the mouth, giving your rabbit time to chew and swallow each mouthful to minimize the risk of aspiration occurring.
(Syringe feeding info in link)
https://wabbitwiki.com/wiki/Medicating_your_rabbit
https://wabbitwiki.com/wiki/Veterinary_emergencies
https://wabbitwiki.com/wiki/Gastrointestinal_stasis
Do you know what medications were given to your rabbit before or right after the surgery. Were any other antibiotics given, orally or injected, and which ones? I'm concerned with your description of there being a lot of white mucous in the poop. Mucoid enteritis can develop into an even more serious enteric illness, and hopefully that hasn't happened.