My periods are abnormal and I don't know why! HELP

Hi, I was wondering if any of you ladies could help me out. I'm 17 years old, just became sexually active about a year/year and a half or so ago. My periods, which used to be a normal 28-30 day cycle, with 5 day long periods, have become pretty wonky. My periods last for about a week at the least, and my cycles are anywhere from 38 days long to 45 days long, sometimes more. I was wondering if anyone has any idea what could possibly be going on, or if this is normal. (Please don't say go to the OBGYN because I know this, I just have a very very full schedule around babysitting, work, school, and school activities. I've been trying to persuade my mom to take me). Any guidance would be appreciated!