Hello, Thanks for writing to Health Care magic, I am Dr , Muhammad Ahmad , I have read your question closely, I understand your concern and will be helping you with your health related problem. Because of this hydronepherosis you are having pain and urinary pressure you will have to get it treated by a urologist. Cause of it can be anything a stone which used to be stuck there but no more there, but it infalammed that part where it was stuck and there was a stricture formation causing narrowing. THere can be many other reasons like locat infection external pressure etc, I would suggest you not to panic and contact your urologist to get it treated, this will also relieve hydronephrosis and your pain. I hope this answered your question, If you have more queries I am happy to answer you. Regards. Dr.Muhammad Ahmad