I have had a dull pain on my left back side about waist level for a couple of weeks, oddly only while I sleep (feels kind of like a sore muscle but forces me to lay on my left side. I also noticed my stool has been green on occassion (twice) over the past weeks. I am taking Tamoxifin and have had weird responses to the medication . First 6 months terrible constipation , never had this problem prior and also larger stools . May not be related but thought I would mention it.