Baytril isn't always the best antibiotic to use on infections in rabbits. And it sounds like if it was working in the beginning, its not anymore since the infection is worsening. I would want the antibiotic changed. A culture and sensitivity test would give you a better idea of which one to use, but I wouldn't want to wait around for the results before switching antibiotics. I'm not going to sugar coat it, your rabbits condition sounds fairly critical, and at this point even changing antibiotics, I'm not sure if it can be turned around. So going ahead and trying another antibiotic is something you'll need to determine if you feel there's still a chance to turn this around, and if your buns quality of life is still there.
So without a culture and sensitivity done, I would want to get my bun on pen g procaine/benzathine injections immediately. It's a combi pen, not just single pen g procaine. Your vet shouldn't charge more than $15-25 for a 100ml bottle. If they do then you can get it online as Combipen or at a livestock feed store. Your vet should show you how to administer the sub q injection. You'll also need the correct syringes and needles. I would want to give the injections every other day at least, possibly every day at the start, based on the info in this study that was done.
http://people.umass.edu/~jwmoore/bicillin/bicillin.htm
http://www.bio.miami.edu/hare/jawabscess.html
I would also consider adding in oral azithromycin. Just because you need to hit this pretty hard now, and those two antibiotics seem to be the most effective on head infections.
Here's info on adding in the azithromycin. Randy is an experienced member that used to post on here a while back. If you want to gather more info about using the azithromycin with pen g, just go into his postings. There is some risk with this antibiotic though, as in some rare instances it can cause severe digestive upset. So it's a matter of weighing the risk with the severity of your buns condition now.
https://www.rabbitsonline.net/threads/pen-g-vs-bicillin.29133/