Its normal to miss periods or be late on them from time to time. Stress, weight loss/low body fat content, diet change etc can cause a delay with your period.
Two months ago, my husband got laid off, and I skipped my period that month. If you are on birth control they are usually more regular than if you are not, but that doesn't mean it's abnormal for it to be late from time to time. Try not to stress, that wont help with how you feel and your period delay!