First, call your vet that you’re seeing on Monday and see if she has an emergency phone number to call if she doesn’t answer. If yes, call that number and describe your bunny’s condition over the phone. If she has an answering machine and you haven’t booked the appointment yet, leave a detailed message describing everything, and say you will be bringing him in first thing Monday if you can’t see someone else, but please call you back to let you know what to do until then. Leave a call back number.
If that doesn’t get an answer, call a few general vets from the yellow pages that are near you and ask if any vet working there is experienced with bunnies. One may be, and again, describe the bunny’s condition. Tell them that you can get him to your regular vet on Monday if need be, but he seems to be in pain so you would like to know what to do until then.
Often a vet Hospital has a larger capacity for seeing different kinds of animals, so try them first.