Period Cycle Crazy

My period is always so irregular and all over the place still. I got it when I was 12 and now I'm 20. I get it every month but the cycle length varies so much it's always a surprise when it comes. I never know when to expect it. It also gets in the way of D appts and stuff cuz I have to basically block off 2-3 weeks of time that I can't do anything just in case it comes any of those days 😭😭😭😭 what do I do?? 😩😩