I think you should bring a stool sample in to your veterinarian to have it checked for parasites. I would also suggest that you schedule an appointment with your vet because there could be a systemic disease that is causing the diarrhea. The odor could be a sign of a serious problem. As for things you can do ...... Probiotics can help with diarrhea. There are homeopathic remedies that can improve diarrhea, but I would need a few more details to help you find the correct one.
Please let me know what your veterinarian finds and then I can give you more holistic suggestions.