What is going on???

I started the depo shot the 12th of September and then I started my period the 4th of October and it lasted until the 15th of October which isn't normal for me because my periods usually last for 5-6 days but my last one was about 2 weeks long. Anyways, I had unprotected sex the 18th of October and I let my SO finish in me because I had been on the shot for more than a month and he had asked about it and now my period is 7 days late. I was supposed to start the 2nd of this month and I'm always regular. I asked my doctor about it and she said it was probably because my period was coming to a stop since I'm on the shot but now whenever I go to the bathroom and I wipe, there's like a light brown color that comes off onto the tissue like I'm coming off of my period, so is that normal?