There are several synonyms for the phrase "go on and on". One of the most common synonyms is "ramble" which refers to the act of speaking or writing at length about a particular topic without clarity or purpose. Another synonym is "drone" which denotes a monotonous or tedious tone while speaking or narrating. The phrase "talk endlessly" is also a suitable synonym. Additionally, you could use "rant" to describe someone who speaks at length about a topic in a passionate and often angry manner. Other synonyms could include "keep talking", "continue", "persist". Using a variety of synonyms will make your language more vibrant and descriptive.