Fast starting October 21 days

Hi there,
I am 40 from Australia and looking to do a fast, not sure how long i want to fast for maybe 21 days to start of with then extend it. I am afraid of not pooping for that amount of time and refuse to use enema’s. Can someone please share weather or not they had issues with bowls on a fast and how long did you do it for?
Thanks. P.s if you want to be accountability buddies please inbox me.