Are you my twin, just living in a different house? (smile)
Absolutely, and it could be your kidneys - make sure you drink PLENTY OF WATER. Call your doctor and let he/she know you are having symptoms. They may want to do a urine/blood sample. There are many within this outlet who would know better than me.
Since I am at near Stage 4 in my Lupus Nephritis, I've had more than a few episodes of the left mid-lower back pain.
So drink up girlfriend, and think about calling your doc - just to make sure.
Life is good, love is better
p.s. it's so good to know that we're not alone, isn't it?