Diarrhea can be stress related. We have a patient who gets so stressed out when brought into the vets office, within about a half hour he starts to develop diarrhea. So, yes, stress can be a factor.
You may also want to try giving your pet lactobacillus/acidophilus on a daily basis(not just when the diarrhea develops) This helps to balance the intestinal flora.
Another thing to consider is better treats. Ones without wheat(as wheat is not something a dog was meant to eat, but is found in most treats such as milkbones and some foods. Also, the beggin' strips are loaded with dyes and preservatives. If you are looking for an all natural treat, try to go to
www.henryandsons.com
They have all natural cookies made with organic ingredients. My favorite one is apples and oatmeal biscuits.