Unexplained fevers for 20 years, rashes, negative ANA

As title states I’ve had low grade fevers chronically for 2 decades. I have a persistent r ash on my chest that gets triggered by sun/heat and gets very itchy. I have interstitial cystitis and IBS.

Routine blood tests and ANA have been negative. The only test I remember being positive that my primary ordered for me in conjunction with my fevers was a high sedimentation rate. I know I have inflammation in my body. I just don’t know what’s causing it. I am currently in a flare with fever every day feeling so miserable and I’m tired of not knowing what’s happening in my body or how to treat it. My fevers sometimes last a month, come and go.

My father had RA. I was denied seeing a rheumatologist before due to negative labs. What tests are definitive for autoimmune disease? I would appreciate really any advice from this community on what to do next - I don’t know what to ask my doctor for anymore.