Talk to Urologist on Left Flang Pain

I experience pain in my left flank (on the back side) since 3 4 months. Although the pain is usually not severe, it's noticeable in the mornings and tends to decrease gradually throughout the day. I have had an X-ray of the KUB, an ultrasound of the KUB, renal function tests, and a urine test, all of which came back normal.

I was also deficient in vitamin D (19.6 ng/mL) and was taking 200,000 IU every two weeks for three months. What could be causing this pain?