Is diarrhea considered to be a symptom of getting your period?

Occasionally. When the period is coming a few women will get diarrhea. This is from a chemical the lining of the uterus makes, called prostaglandin. This chemical can cause diarrhea, nausea, and menstrual cramping.
Sometimes. The hormonal changes associated with the menstrual cycle have been associted with changes in bowel habits and are a common cause of irritable bowel type symptoms. These can often be controlled with medications and occasionaly with dietary modification and the use of probiotics.