Hi Doc I'm 26 Years And My Periods Was Suppose

Hi doc I'm 26 years and my periods was suppose to be on the 11sept but nothing after a week I did a pregnancy test but it was negative I waited for anather week and did a test again and still negativeon the 3rd oct I did a third one still nothing iam worried becouse I have been feeling tired and I go to the toilet all the time and in my penti liner I sometimes see a brown discharge and I'm having a back pain and headache and my nippels hurt plz help no food cravings