My buns never had a reaction like that to metacam either. There were times my bun had to have something stronger for a few days. Anytime I heard her making any noise, laying funny, and not moving as much I used the buphrenex.
I have done sub q's and I hate it but it goes so much quicker. I could give 150 ml's in 15-20 minutes and that was usually the dose for the day. So once that 15-20 minutes was over, as bad as it maybe, we were done with that for the day.
Are you soaking the greens you are giving? I know it may not seem like a big thing but it has really been what has helped saved my bun. When she was really bad and wouldn't eat unless I hand feed her the greens. I would put some in a tupperware container with water by her cage. Every 30-60 minutes I would go in and take a piece that had been soaking and try to feed it to her. It was easier then going to the kitchen everytime and every piece she ate out of my hand was dripping with water.
I am glad your buns x-rays showed improvement. I know how frustrating this can be. I have been dealing with this on and off since October 2008. You will find what works best for you and your bun. You are doing a great job, keep it up.