My boyfriend and I have been sexually active for a while and I have been on birth control for about 5 months now. Ever since I went on birth control we stopped using condoms. About two week ago I forgot to take my pill and I forgot to double up the next day. After I noticed I forgot to double up I just started over again from start. It has been two weeks since my period ended and yesterday I noticed that I had brown spotting on my underwear.

Im not sure exactly why I had the brown spotting if any one has an idea can you please let me know? Please and thank you!!!