Hello. I'm Nida 24y/F. I Have Been Diagnosed With Sacroilitits

Hello. I'm Nida 24y/F. I have been diagnosed with Sacroilitits recently. ESR is 50 and ASO titer is 302, vitamin D is 13 and with normal CBC. MRI shows normal SI joints. My neurosurgeon has advised me to take corticosteroids. I still have inflammation and severe pain in my si joints, it's been two months.

My question is what is the cause for my condition, does streptococcal infection causes Sacroilitits as my ASO is high? And if yes how is Sacroilitits caused my streptococcus treated? Do I need to get some other blood tests to confirm it?