Xanax and fibromyalgia

Xanax is much maligned but was my saviour after having a total personality change with the onset of undiagnosed fibromyalgia. I held out for 18 months. I have taken Xanax for 8 1/2 years now and suffer no bad side effects except I'm sure it has helped me gain 30kg!(depressing in itself). Doctors don't seem concerned that I have taken it for so long. In fact a few have said I will probably be on it for life (a scary thougt for someone who hates having to rely on drugs but has to have a life). I have had a couple of dodgy liver function tests and have to have another one. This, I wonder, could be a side effect of long term use of Xanax? Is this harmful? Any comments welcome.