Early period

So my period is 1 week early but i think the bc is tricking me into thinking im prego. Started it 3 weeks ago. Stopped taking it 2 days ago due to side effects and have an appt fri for poss mirena. I had some brown/bright discharge kind of like when you are prego. I took a test but it was neg. I have had a false neg in the past. Any suggestions or other experiences with this?