Have you seen a Gynecologist? Stress plays a factor in late periods but if you don't have a period for more than 3 months then you should see an OBGYN.
Your period can be late for so many reasons I can list for days! Missing a period is usually no cause for concern, especially if it's happened before. That being said, I would discuss birth control pills with your guardian and doctor, they help things to stay on track, so you don't have to worry about them being irregular. It's worth getting checked out at your doctors office just due to the fact that there is so many reasons this could be happening. Most women's periods run on a 28 day schedule, but that isn't true for everyone, and it doesn't mean anything is wrong, so in the mean time try not to worry about it, but look into some solutions with your doctor :)