Differences in Testicle Size in 5yr old

My son is 5 years old and at this time is quite large downstairs. Well atleast to a point. You see, his right testicle is about the size of a golf ball. While his left one is pretty much the size of a very small marble. I said something to the doctor when he went for his Kinder. evaluation but the doctor simply pulled out his pants and looked down. He said that it was fine. But How does he know, he didnt even look at them. I thought that maybe the one just hadnt fallen yet but when I felt them it all there. Its just extremely tiny. My husband seems to think that since he is not in pain everyday then there is nothing wrong. However Im his mother and you cant tell me that its normal for them to be that uneven. I mean its almost 100x bigger. He knows that something is different about them. Every time I give him a bath he points them out and asks me about them. Someone please help me, help him.