Bleeding for 3 weeks?!?!

So my periods have been really off for several months, I haven't been too worried because my mom told me her periods were like this until she had her first child. I would sometimes have 2 periods in a month or have my periods be really unevenly spaced out. But October has made this very concerning. I had my period at the very last week into the very first week of october, totally normal, but then barely a week after, the 19th I think, my period started up again and has been going on ever since. I have an apointment with my doctor on Monday morning to talk about this and other things but I was just wondering if anyone else has experienced this or something similar or has any ideas as to why this could be happening.

Also I'll update after I go to the doctor incase anyone else is curious about this.