Very odd question. Please help.?

My father and I were talking about my low testosterone problem and I am 29 and i told him the dr said my testosterone was 219. I told him it was attributed to my one testicle. He was stunned he said one? I said yes . He said you had 2 when you were born and during your physicals. I told him as far as I can remember I have had one and thought I was born with one. So my question is the dr. felt around on my pelvis area and felt nothing. Where did the other one go.