THE AUTOBIOGRAPHY OF MY BODY by David Guy (E. P. Dutton: $19.95; 336 pp.). Newly divorced Charles Bradford, a writer, returns to Pittsburgh to become reacquainted with his father, who has been laid low by a heart condition and who is at the same time threatened by a brewing scandal at the prestigious law firm of which he is a senior partner. It's a period of mutual discovery for both men. The specter of mortality that now hangs over them allows them to talk to each other as they never really did before. At the same time it's a period of "Who am I?" and "What am I looking for?" for Charles, still on the rebound from his divorce, who finds himself drawn into a torrid affair with the lusty Andrea. Be advised: You might think twice about leaving this very adult novel on the coffee table if dear Aunt Mildred is planning to drop by.