If we are counting what I sleep in, at least twice. Tighty whities or boxers during the day, and then another pair of baggy white boxer shorts to sleep in.
Depending upon what I am doing during the day I might change again. If I start the day in tighty whities I usually change out of them into boxer shorts to lounge around in for the evening. Depending upon what I am doing and what the temperature is I might change into a fresh pair of tighty whities during the day. I don't like sweaty underwear (for that matter I change t-shirts, too) and it is easy enough to do laundry.