Bleeding

So I’ve been on lessina pills for the fourth month now a week ago I had been forgetting to take my pills but took one in the am and one at my normal time (night) a few times. I had a little bit of old brown blood with my discharge for a few days and today when I was at work I had a breakthrough bleeding and it was very red but I don’t start my period until next Saturday, can someone explain to me what’s going on?