Thanks so much for you answers (:
Put vaseline on your bottom after each bowel movement to stop the irritation and burning and call your GI doctor. Take care.
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.