Being a little irregular with your period is pretty normal. At 14, you will have a body still adjusting to hormones and what they do. You can even skip ovulation in a random month, and that means you will skip the period that would have followed. (Ovulation prompts the following period, not the other way around.) If you would like, keep a chart on graph paper of the days of your menstrual months (or use an online chart) -- sometimes women assume their period is supposed to come on a certain calendar day without remembering that it is supposed to come on a certain day based on the first day of the previous period (such as, every 28th day or every 29th day from the last period).
If you've got all that right and are sure you're 4 days late, just wait and see. You could have an ovarian cyst, you could have skipped a month ovulating, you could just be a little late because something shifted your body's timing. (Sometimes women's cycles shift to coordinate with other women's, like, when a woman moves in with roommates in college, they all often begin to cycle at the same time.) If you have low body fat, your periods might stop. Stress can also stop periods. None of those things are a very big problem.
If this keeps going for a couple of months more, see an ob-gyn. But my first guess is that you're just a little late.