Period question!?

So my last cycle I spotted for roughly 2 weeks straight. Mostly brown blood but occasionally a small amount of red. I'm on my last day of my period right now. Any idea why that happened? I haven't had sex in over a month. When I went to the doctor I was told to wait and see if I kept blessing 2 weeks after this period to come back and if it stopped on its own them I was fine. -_- (military doctors) Anyone have ideas? Has this ever happened to you?