Why am i having Brown discharge ?

I've been having this brown discharge for 2 weeks now and its not going away. I took a pregnancy test at the clinic and it said i wasn't so I'm sure that can't be it. i don't know if it has to do with the birth control i use to take (i stopped) but it's starting to worry me. I'm praying the pregnancy test wasn't wrong but i honestly don't feel no difference so i know im good with that but i do want to know why ive been having this brown discharge for so long .. PLEASE HELP ME :/ Thank you