Struggling to Get Doctors to Take My Symptoms Seriously

I can’t shake the feeling that something more is happening to my body even though all my tests keep coming back normal and they keep saying if there is no visible swelling that they can see then there is no problem, even though I do get occasional joint swelling, redness, and heat when my joints ARE in pain. The typical fibro symptoms that bothered me in the beginning like widespread muscle pain are now taking a backseat to my severe joint pain. A specialist told me my joints were loose and said it was normal to be flexible when you are young and then get stiff as you get older and then pretty much sent me on my way. I have symptoms of many other autoimmune and chronic conditions that I suspect I may have as well, but every doctor I have seen just continues to attribute any and all symptoms to my fibro. To anyone who has been diagnosed with another condition after first being diagnosed with fibromyalgia, how did you get doctors to look further and take you seriously?