Just posting an update. So ... i am not 100% sure of this but after 4 days the flagyl didn't help. So I started to wonder some stuff.
I am also currently in physical therapy for a lumbar disc bulge (and a cervical spinal bulge, too) which is like a pre-herniated disc. I found this out about a month ago and it is possible the tailbone pain is from that, and not the pouch. I've been having problems emptying...as in it's been difficult, I'm constipated, but the stool isn't particularly dense. It's basically it's normal consistency but difficult to get it out.
I had much less pain when I did more exercises from PT for my lower back. I'd been focusing mostly on my upper and mid back because there was more pain there initially than the lumbar but now the lumbar is the one that hurts, probably because I was ignoring it for the upper back. After a few days of focusing on that, I feel a lot better. Still constipated but the tailbone feels 99% normal.
I feel like I am a living construction project...tightening one bolt loosens another, and tightening that one loosens another one. At some point I'll be all screwed back together...maybe,...