Yup it's usually from the kidney pain/swelling(I go into kidney failure when I flare).I start my flares with non stop nausea,decreased to non existent appetite,foamy urine,constipation,swelling,decreased urine output,urinating a lot at night,skin texture change,hair becomes hard/brittle,hair loss, migraines,extreme fatigue,sudden bruising,breathlessness,increase light sensitivity,a weird after taste,and I just generally feel really weak

Lower back hurts almost always, I feel ill (flu-like) quite often. GI tract kicks in when in a flare. Fatigue - it's getting really old.

Mine always hurts. I just feel stiff and to weak to pick anything up.

Yes, i always do. The only thing that works for me is prednisone and SI injections. I am HLA b27 positive too. My back gets stiff and i get stuck trying to stand up. Feels achy and heavy when standing.

Yes! OMG it always starts on the left side of my back and it causes me to have trouble breathing. Usually lasts a few hours then will go away
Sometimes I try to do stretches to help alleviate the pain faster.