Every now and then I have a sharp stabbing pain in my lower left back, around the love handles. It stabs then goes away, maybe once a day for 3 weeks?

Maybe? If there is no other problem, I'll suggest that a nerve is not at ease with some muscle in the area. The sciatic s common, bt there are less well known ones too. Some position or movement you make a lt or one that was a bad one may have caused it. A massage may help - or PT - yoga - expert gym trainer. best!