Left lower abdomen and flank pain.

I have had left lower abdomen and left flank pain started in the month of January 2020. At that point in time it started with a burning while urination with radiating pain in the left groin and left knee.  I have had a urine test without culture and sensitivity and an pelvic and abdomen ultrasound done with almost normal result apart from slight left PCS dilation and the radiologist told me it could be due to a stone or an infection and doctor recommended me 15 days of antibiotics..This helped a lot to subside the pain to about 99.9%..I had stopped taking refined sugar and any other processed foods also...everything went well for approximately 1 month and then the pain came back with additional pain in the lower back..wondering is it possible that the infection is still lingering without complete resolution. What it could be..please answer..