Okay, I had my period August 18-22. According to an app I have on my phone my ovulation after that period was August 29- September 3. My highest day of fertility was September 3, 2012. I had protected/safe sex before my highest day of fertility & the whole month of August I took my birth control correctly. According to the app on my phone, my period was suppose to come September 18, but it didn't. Here it is September 22, and I'm still not bleeding! Could I be pregnant? Or did my period just skip because of the weather changing & all of that?

4 days late is not abnormal. Stress can cause a late period.