Chronic pyelonephritis involves injury to one or both kidneys as a result of recurrent or persistent kidney infection over a period of time. It often results in progressive damage to the kidney, resulting in an irreversible loss of function. It is known to occur in people who have an underlying anatomical abnormality, such as a urinary tract obstruction, large kidney stones that persist or, most commonly, reflux of urine from the bladder into the ureters (which occurs mostly in young children).
Based on the information provided, it seems that chronic pyelonephritis may have resulted in the right atrophic kidney (small sized kidney from the chronic kidney injury). You certainly require a thorough investigation of the urinary tract through imaging tests to detect the cause for the recurrent bouts of urinary tract infection (which probably resulted in the chronic pyelonephritis affecting the right kidney). This would also help minimise the risk of damage to the left kidney that seemingly remains spared until now. It is rare for men at your age to have recurrent urinary tract infection without the presence of an underlying anatomical defect or an obstruction in the urinary tract.