Some girls are naturally irregular. If you're concerned, see your doc, but I'm sure it's nothing to worry about.
Worth getting checked out by a doctor.
Could be a bunch of things, many of them are not problems, other could be. In my own case, I had similar problems while over-training as an athlete. Adjusted training and nutrition and the problem was gone.
Not every women is regular
If you're worried go see a doctor
consult with your doctor
Fairly common; if you are worried see a doctor that is what they are for.
Had it always been like this or just recently? A lot of ways it can differ: change in diet/eating habits, change in exercise, stress, rapid weight loss/gain. Just some possible examples.
It can take years for females to find a rhythm with their periods. Mine only started getting regular this year and I'm 24
some females are just not regular naturally . in my experience, i was not regular when i was younger , now i am . it's good to go to ob-gyn once a year anyways and your doctor can figure if it's just that you are irregular or have a hormonal imbalance or something.