is unlikely to be a side effect of most medications that are used for allergies. In fact, many of them can have the opposite effect, although the majority of them tend to not interact with the bowels to any great degree. The nice thing about your current situation is that you can quickly test whether or not it is the medication by simply discontinuing the medication, or switching to another. Allergy medications are hardly vital to life, and there are many options available. This sort of "empiric" approach is often valuable when there is a limited number of variables that you are considering as the cause of your problem. That being said, if your diarrhea has continued for some time or is threatening your hydration status, you should speak with your doctor
. You should also make sure to be very careful to wash your hands repeatedly, as most forms of diarrhea are very contagious. Good luck, and please do discuss this issue with your doctor soon.