Unless it's just outright really loose stools or diarrhea, it's actually very healthy for people to have 2 or 3 BM's a day. Perhaps inconvenient, but healthy. If you choose to stick with the arimidex, just make sure you are getting well hydrated and eating plenty of fiber, and I think you'll find the increased frequency of BM's is not a problem.
If you don't want to stay with the arimidex, check back through past message threads on the board - there are lots of suggestions on how to get through this without all the nastiness of these drugs.
Sincerely,
Tre