I'm sorry you have to battle this rotten illness that affects the person in so many different ways but you're right, there is no known drug cure and many people take that realisation as meaning nothing else can be done!
As someone once said, carry on doing what you're doing for exactly the same results.
I notice you have been to the fibromyalgia pages on our website and I can't add a great deal to the information already out there so the key thing is to prioritise your personal symptoms and address the most irritating of those before looking to get to the root of the issue.
Pain and sleep deprivation don't set you up for a good push on the dietary front, for example, so if pain and sleep issues are your biggest hurdles, get them sorted so you have the strength to look ahead to the next challenge.
Regarding the exercise, please, please keep going. Stretching, yoga, swimming and Tai Chi are the perfect antidotes to doing nothing as inactivity will result in both stiffer muscles and lower mood. Keep it mixed up, with different walks to prevent staleness and catch the last of the summer rays because it's harder to stay motivated come the winter.
Without a consultation, I can't have a good pick at your diet and lifestyle, so try keeping a food diary for just a week and with a bit of honesty, you'll be able to see any naughty habits and whether a worsening of symptoms follow certain foods. Most reactions to food occur within 2 hours (about 90%). The other 10% are harder to spot as they take 2-48hrs to show, a big window. It may be worth noting how well you slept each morning too, so you can see if anything you eat affects your rest.
Ask a friend or partner what they think you complain about most if you're struggling and you'll have a good starting place.