I am having on and off pain on my lower left side. like its.cramping you getty while running. mostly after my period and then it shifts.to my right?

Mittelschmerz: While this could be endometriosis, it is more likely mittelschmerz or ovulation pain. If it is occuring 10-14 after your period starts and lasts for 2-3 days. Women with ovulation pain will often times have it on one side one month and the other side the next month, though most women tend to ovulate slightly more often on one side or another. More information about your pain is really needed.

Try this: Not likely ovulatory as that pain would stay on one side, although if consistently at the same time of month and only for 24-48 hours then maybe. Shifting pain like that will usually be bladder or bowels. Stop caffiene and acidic beverages, if no response see a gyn.