I'm 20 years old. My periods usually postpone for 5 to 10 days every month. All scans and blood tests are normal. But thus month my periods postponed for upto 16 days and when the flow started it was dark brown in colour and even had a sour odour which I have normally never experienced over the years. I have no pain no fever. What old possibly be the cause? Is it normal? Please help me out. The bleeding is happening at a slower rate too.