4 months and no period

So I haven't had my period since November. I'm 18 and a virgin, so there no chance it's pregnancy. I've been to the doctor before and they've said there was nothing wrong (could be stress induced). This isn't the first time, but it is the longest. When I do have my periods, they're anywhere from 3-5 days long, not overly heavy and I rarely have cramps. I'm pretty sure it's a mix of bad eating habits (starve/binge plus waaay to much sugar) and stress. I am overweight (5'8" 210lbs) but I've had blood tests and everything came back fine.