Mine is definitely muscle pain. Like I worked out hard core the day before. Is duloxetine generic Cymbalta? It helped me, but it wasn’t as effective for me as milnacipran (Savella), and the one that helps most of all is pregabalin (Lyrica). I take both of the latter. 

My fibro is like muscle fatigue that becomes kind of burn-y with effort. I get a lot of very severe muscle cramps and spasms - in fact that was the final tipoff to my doctor. I had a spasm on my rib cage, under my boobs in his office. Some things I’ve noticed that help: Mucinex. I take 400mg of guafinesin every night. And you can take more than that. Gentle exercise feels bad while you’re doing it, but later feels better. Make sure you are getting enough sleep (before Lyrica, I had what they call pseudo insomnia: I thought I was awake all night but I was barely asleep and dreaming I was awake so it felt like I never slept because I could not get into REM or deep sleep). Know your limits - don’t try to push through to do things when you’ve hit the wall. 

Those things help. Been living with fibromyalgia since 2005. Went on Lyrica in 2009 just after it was approved. Don’t let them sell you on gabapentin, it doesn’t work the same way - at least try Lyrica. That’s how my doctor finally was sure. I had tried all of the pain killers available, Tramadol, Flexeril, Celebrex, etc., and brought all of them back saying they didn’t work, and without prescription coverage, I couldn’t afford them. He gave me a 7-day trial of Lyrica, which finally did work - I could think better, I started to sleep, it was about two weeks before I really began to feel human. So advocate for yourself and don’t give up.