Although it is very unlikely for someone to get pregnant if they had protected sex, it is not impossible. So it would be a good idea to get a
pregnancy test just to make sure you are not pregnant. If the test is negative, you might need to wait another week or so and if you still don;t have a period, repeat the test, as it may be a little too early right now for the test to be positive.
However, it is also possible that your period is simply a little delayed. Even people who are usually very regular can occasionally have a period that is late, or even missed. This can happen due to
stress, illness, medications, or to random
hormonal fluctuations. If this is a one time event, there is nothing to worry about, but if it is persistent, you can see your doctor to discuss testing to figure out what is going on. There are many possible causes, and a full workup by your doctor would need to be done to figure out the answer. Please let me know if you have any more questions.