A) IBS waxes and wanes. Most people will find that they do have flare ups that will give them symptoms even when they have good control almost all the time.Having IBS doesn't protect you from getting something else. When you have a significant treatment failure (particularly if it lasts more than a day or two) it is time to go back to the doctor and see if it is an IBS flare up, or you have something else. After all we still get food poisoning, histamine reactions from improperly processed fish, stomach viruses, parasites, etc that cause diarrhea in normal people.It is one thing if it is a few days of problems vs a treatment failure of more than a couple of weeks.You will have diarrhea ONCE in awhile (sometimes for days to a couple of weeks)EVEN if you didn't have IBS.C) Sometimes even when someone has been on a treatment that worked for years they may need to alter the dose. Things do change in the body over time so it may be time to talk to the doctor and see if a dose change or perhaps a medication change is something to think about.K.