i placed my son up for adoption

I had a son that was born on September 25,1976 and I put him up for adoption. I thought I knew who adopted him. But I am not sure. In 1978 I had to have a operation and the Doctor who did the operation had told me he had 2 children. A son that was adopted and a daughter that was not. I asked when his son was born and he said Sept 25, 1976 at Hinsdale Hospital. I said my son was born on that date at that hospital. All these years I thought he was with this Doctor's family. And I contacted him a couple a years ago. He denied the whole story. I believe in my heart he did adopt my son. But cannt find out any information. I am looking for any suggestion as to what I should do next.