I have recurring lower left abdominal pain...mild to sometimes severe. missed and very irregular periods. what can be the cause of the pain?

Many possible causes: There are many possible causes. Please see a Dr. for an exam and, if needed, testing. This will help find the answer. Once you know the diagnosis, the Dr. can help with treatment.

Abdominal pain: Your pain may be due to diverticulitis/diverticulosis cause by constipation. However, it is best that you be seen by your doctor for a definitive diagnosis