I thought about stress but honestly I'm not stressed over anything. I mean some days my daughter drives me nuts but that's it, I haven't been on any medications except my pills. When I was pregnant with my first baby I missed 3 periods before the pregnancy test finally came back possitve.
From what you have said it is most likely to be something else - stress can cause a delay or absense in your periods. Although you havent missed any pills, have you taken any anitbiotics recently as this can stop your pill from being effective.
Stress? Don't know what else it could be. You could definitely be pregnant and the test is not picking it up. Anytime you have sex you have that chance, with or without birth control.