Hello Jennifer,
It’s common (especially for women) to not be HLA-B27 negative. X-rays and MRIs are important diagnosis tools. Hope you get some answers.

Blood Test!! I was diagnosed aox.6 years ago only because I myself went to a doctor and asked questions. Now I'm on Cimzia shot bi-weekly. But still do Blood test every 6 months.

Can you post a pic of X-rays?

AS usually starts in the SI Joints. Do you have SI joint pain? Low back pain? Pain bending over? Buttocks pain? Joint pains?

It certainly sounds like you have an AutoImmume Disease but if you don’t have SI joint pain, it might be something else. There are a lot of AI diseases. And find a Rheumatologist that will look into it throughly.

I am negative for genetic markers, but do have symdomorphytes with fusing in the thoracic area. Rheumatologist Dx me with AS without any issue. Good luck getting the care you need