kidney problem in 20 month child.

Hi,
my name is prya and i have a 20 month old son when he was 2 months old he had UTI infection so we went to see the doctor he told that he has only one testicle so docters suggested us that we see a uroligest by this time my son had 3ultrasounds and 1 reflextest of some type and every thing was normal with him except his testicle, the docter said that we should get it fixed so there is no problem when he grows. So in Jan.2004 he underwent surgery and it was doen, The docters told us that his other testicle got twisted so it did not develop. But when we went for his followo up appointment after 6months thay told there is some kind of fluid in his kidneys, which were totally normal before. So doctor told us to wait for 3 more months and have another ultrasound and see how he is doing. I am worried sick that what should i do now , how he ended up having problem in his kidneys . It should not be happning. I am confusied and dont know what to do please help me.