First sexual relationship and irregular periods

Hi -

Any words of wisdom or comfort would be sincerely appreciated.

I'm 24, and have had a period by which you could set your clock for 14 years. For the past 2 1/2 months, I have been having sex regularly for the first time. My boyfriend and I (very carefully) use spermicidal condoms. Since we began having sex, I have had two periods. The first one was normal (this was right after we began having sex), but the second was 3 days early. I was due for my next period yesterday, and not only has it not arrived yet, but I don't feel signs of it coming, either.

I realize that to be frightened of pregnancy at this stage of the game is irrational, because it's only 1 day. Still, though, getting pregnant would be catastrophic for me, so I am admittedly anxious.

I should also mention that I've been experiencing a tremendous amount of stress at home with my family. I have considered that this may have played a role in my period being messed up. My boyfriend seems to feel that, because this is my first regular sexual relationship, my body might just be adjusting to that.

Please let me know what you think.

Gratefully,
Jennifer