Should one be concerned about the whispers (waswas) that make one feel as if gas is being expelled from the anus during prostration (sujud) and bowing (ruku'), especially if this increases after overeating?

Do not pay attention to what you imagine about gases escaping. Your prayer is valid, for it is stated in the Hadith: "He should not leave until he hears a sound or perceives a smell." And hearing and smelling are not conditions, by consensus.