Pregnant or paranoid?

I recently started having sex with my first boyfriend. We usually use condoms but on day 33 we had unprotected sex, with the pullout method.

I'm usually 30-38 days for my cycle. Lately my periods have been very irregular, like in the past 4 months. (I didn't lose my virginity until a week ago though)

I'm now day 37 on my cycle. I feel cramps every now and again, like my period is coming, but I'm still worried.

I took a Plan B pill after the first time (even though we used condoms) because I was horrified of being pregnant. I've heard Plan B can mess with your period.

If you've ever used Plan B pills, can you please comment if you've experienced a difference in your period that month?

Last night I had cramps so bad I was SURE I had started my period but it's still not here. I'm starting to truly panic.