I Am A 87 Year Old Male, In Good Health,

I am a 87 year old male, in good health, but yesterday when I lay down to take a nap I could not sleep because of a dull internal pain on my right side at a definite place around my waist-line. It only occurred when I was lying on my stomach or back. Last night the same thing accured and kept me from sleeping for several hours, them subsided some. Today (Monday, Oct. 24) the same thing occurred when I went to take a nap. I have never had my appendix removed. What are the possible diagnosis? Dwight F. Zeller