Back Pain maybe sacroiliac joint ?

Hi FB family,

I need some advice. Since Thursday last week I have back pain in my lower back. But not really the spine, more left and right from the spine and more on the "bone" of my pelvis/hips. After asking doctor Google I learned that it might be the sacroiliac joint. Never heard of that before ... When I stretch a little it seems to get better for a few minutes, but in the end it stays the same. Does anyone have experience with this and/or knows what to do about it? For today I scheduled a HIIT workout which is not a good idea I think ... Probably I just do some light but longer stretching in the evening and see how I feel. Thanks guys!