Pelviureteric junction obstruction occurs at the junction of the renal pelvis i.e a point where the kidney drains into the ureter. The obstruction at this junction can occur either due to narrowing caused by previous infection(stricture) or a tumour or it can be congenital(By birth). I suppose considering your age yours might be due to infection. The next logical step would be to evaluate the cause for obstruction and also the functional status of your kidney. The cause can be evaluated by doing a CT scan and function status cannot be evaluated by giving a dye through your arm and taking serial xrays of your kidneys(procedure is called intravenous pyelogram) or by renal scintigraphy(nuclear scan). I do not advise you to leave it to a natural course as it is a mechanical problem and will not relieve by simply leaving it to a natural course. It is only going to get worse. I suggest you to consult a urologist and discuss the management options like diagnosing the cause of obstruction and possibility of correcting it.