I have had FM for 25 years, and yes i have bladder problems too, but i can go continously, full or not, but suffer with pain if i get full.
Fm seems to affect many areas.
Just pace yourself, rest when its bad, and do things a bit at a time, because you will suffer for days if you overdo things
I don't have fibro, but I have CFS. I just know that I am constantly needing to drink water and I often feel dehydrated, although I shouldn't be.
I had a bout of infection issues pre-cfs and read about intercytial cystitus (I know I didn't spell that right) which is more common with CFS than average population. It's a painful hypersensitive bladder. There was a book in the library by a woman urologist in california (the first woman UR in CA) who had effectively treated most of the people who came to her and described it all well in the book. I found the UR docs I went to were clueless, so if you do some research on your own you might find better data than the docs are giving you. The URs tended to do the same pat set of tests on the bladder and if it didn't show anything they had nothing more to offer. Although some offered "training myself" which I knew wasn't relevant.
If your docs haven't already, make sure this isn't involving your kidneys since bladder treatment won't help if the infection or a partial blockage is starting higher up. For the bladder itself, if your doctor hasn't offered a cystocopy yet, it might be worthwhile. On a friend it showed a double urethra (shows up in 5% of the population) that had a lot to do with the infections she was having and in me it showed inflamation and polpys and generally that it wasn't in my head.
For me during my bout of infections what I discovered is that if I took macrodantin I was better in 2-3 days. If I took bactrim or dioxicyclin I was sick for 1 1/2 months over all as well as bladder. Over time I figured out I was having an 'allergic' reaction to some antibiotics. I 'cured' the whole mess by going to bed as though I had a flu and staying there. Over the next few days my body developed 102 fever and after a few more days it broke. It still took a while to fully recover, but that was the turning point. However, I had an infection shortly before that was certainly still an issue at the time or the residual was an issue even though it wasn't showing up on any tests. Also, from the book, I'd learned to wipe myself differently and that small item's made a long term difference in not getting infections.
I don't know how much of this is relevant for you...but for what it's worth.
There was a woman in the UK who had CFS. She died from acute aneuric renal failure, which made it to where she couldn't produce urine. It was triggered by dehydration, as a result of her CFS. A neuropathologist said that the patient's spinal cord showed inflammation and that was enough to convince everyone to list "CFS" on the patient's death certificate.