Talk to Gynecologist on Spotting Between Periods

I'm 36 and married and have 3 kids my weight is 47kgs. I have been using famila 28 for the last 3 years now the problem is almost every 2nd or 3rd month I get spotting or start bleeding between the periods although I take tablets daily at the same time. It also happens when i do some heavy lifting or mop the floor.I have been to many drs they prescribe me duphastan which resolves the problem temporarily.