Anyone get a dull stomach pain when their backs flare?

29M living with ankylosing spondylitis for the past 15 years, doing well on biologics (Simponi).

Whenever I flare it's always one side of my SI joints. Whichever side is painful, I also get a dull stomach pain on that same side. For instance if I'm flaring on my right side, I get this diffuse dull ache near McBurney's point that makes me think it's something going on with my appendix (or some type of referred pain)?

It's weird - it almost feels like my immune cells are attacking back-and-forth between the joints and my stomach, because when I feel that dull ache in my stomach my back actually feels a little better.. but moments later the stomach ache is gone and my back feels a searing, burning pain. Has anyone else here experienced this?

Just thought I'd share this and also ask if anyone else has this experience. I told my rheumatologist but they think I'm nuts. I guess rheum is one such field where every patient is unique, and of course, the lived experience of the disease is more nuanced than just "morning stiffness".

In solidarity - JJ