I get sores in my mouth but I don't know if they are symptoms as well

I looked it up and actually yes it can cause rashes

"Some people diagnosed with fibromyalgia also develop a skin rash. These rashes can vary in size and appear anywhere on the body. They’re most often due to medication side effects and can worsen with scratching. Some fibromyalgia rashes are so sensitive that it becomes difficult to wear certain clothes or sleep. But relief is possible."...

What does the rash look like?

No but I see it a lot in fb groups it's a common symptom