I Started Bleeding This Morning. I Thought I Might Be

I started bleeding this morning. I thought I might be starting my period, but then I looked at the app I have on my phone and it said that I had 8 days until my start date. But I always start 4 or 5 days after the date it says. I've always had irregular periods, but I've never had an early period that was almost 2 weeks early. I'm not bleeding heavy like I would the first day I start my period. Now the bleeding has lightened up. I looked at my first tampon for clots fearing that I might be having a miscarriage but didn't see any clots. But I did notice that there were some bright red blood mixed in. I just want to know what might be causing this.