Period help

So can someone help me?.. I’m 13 and I have very long periods, maybe about 15-20 days or more. January 18 made a year that I had my period for a year. My period just ended. When I had it, it was light brown which means that it’s slowly ending but then it completely stopped. today I had blood , a lot of it, not like spotting or anything, how can this happen when my period just ended? I’m confused because my period just ended literally like 4 days ago and It started again. Why is this?