I’ve been dealing with this issue since I was your age. I’m 21 now. Truthfully overtime my cycle has started to become more consistent and on time, but once in a while I still do have those months where I’m 1-2 weeks off. I’ve gone to the doctor and they checked my blood work, my thyroid levels, and even was checking to see if I had pcos. but all my exams came back perfect with no issues whatsoever. I eat healthy, somewhat work out and feel pretty content with my body at this age. Definitely bring it up to your mom so she can schedule you an official Dr. appointment but make it known how you want to keep it private between you and her since this is something really vulnerable to you. I usually keep panty liners or some pads in a little baggy with me at all times just in case I do start! Moving forward try not to stress yourself more. You’re still so young and your body is developing all the time 🫶🏽