Two missed periods but today I had cramps?

I haven't had a period for two months. The last time I had it was the week I moved into my dorm for college (I'm almost nineteen). I have never actually had intercourse, but I have fooled around with a guy. There was digital penetration, but that's it. Since I moved to college, I've been travelling home every weekend. My eating and sleeping schedule are obviously irregular and there's a lot of stress (the normal away from home stuff, finding out my dad's girlfriend is pregnant, health issues of my family members, class, etc.). I took a test, out of paranoia, about a week or two after my first missed period and it was negative. Normally, I don't get cramps, but today I had cramps. Still no period though. What is going on?