Irregular periods. Why this is so?

My last period was a bit irregular . I had very less bleeding on second day although my period lasted fot 6days a bit longer than normal usually its 5days. Overall bleeding was light. This time on expected date 29sept i had very light bleeding blood that required just one napkin. Then period stopped. Now today 7oct i again have unexpected bleefing just same amount rewuiring just one napkin. Then again bleeding has stopped. Why this is so? My periods have always been perfectly normal although i had an mtp last year. Also i have pain during sex but i have severe coccydynia and i attribute my pain to this condition . But this irregular periods are unreasonable. To me. I dont have unusual vaginal discharge but i m obese weighing 95kgs with 5ft 5inch height