brown period blood in my panties? is that really a period blood or some discharge?

Im 13 and I've been having my period for almost 3 months. This month I haven't had mine except today there was dark brown stuff in my panties . I'm not sure if it's discharge or my period blood. I looked up why period blood would be brown and it said it happens at the end of periods, but this never happened before and i havent had my period this month so it couldnt be the end of my period. Maybe this is the start but im not sure . I put on a pad just incase but i dont know whats going on. Do i have an infection? is this normal?? please give me your opinions