I think everyone is different. My prep didn't work until the middle of the night which woke me up after pooping all over the sheets.
If it doesn't stop within a day or two, I'd call the doc back and let them know.
Keep drinking fluids though so you don't get dehydrated.
Put vaseline on your bottom after each bowel movement to stop the irritation and burning and call your GI doctor. Take care.
Thanks so much for you answers (: