I have been experiencing a brown discharge for 7-10 days now and was supposed to get my period Dec 21st and it has not come yet. I had a pregnancy test a week ago and it was negative and I went off birth control two months ago... my last period was on time and I am very ocnfused as to what is going on. I was on oxycodone and a sulfur medication for bronchitis the past month. What could cause this