Could The Delayed Periods Be Due To Stress?

My last period was May 2(start) ending May 9 2010. Me and my boyfriend used the pullout method and he is very sure he pulled out because he has two kids and does not want anymore. I was suppose to have a period June 2 2010 but it still has not came and it is now June 17. We use the pull out method and Im not sure when I ovulate but I believe my cycle period is (30) instead of the average 28 for most women. I believe I am two weeks late and took a pregnancy test today and it came back negative. Could I possible be pregnant or am I stressing?