I can't be pregnant, can I?

I thought I was going to start my period on Sunday, the 18th, but it never came and still hasn't. My breasts were sore for about a week prior, which is the usual routine when i'm due for it. They are still tender actually. I'm not regular, but I can usually predict when I'm going to get it, and I'm usually right, and I'm never "late". For example, last month I got it between the 12th and 17th I'm sure. Sometimes I get it before that the following month, but never after...like I am now. I've been thinking about this so much, and regretting past sexual encounters. I'm a virgin, never had actual intercourse (we're going to wait for that), but my boyfriend and I had oral sex on the 17th, the day before I thought I was going to get my period. Yes, i know you can't get pregnant from oral sex...but we were messing around a lot that day. We never took off our clothes, although I did pull down my shorts to receive oral. Now, I feel really awful about it and upset. We weren't that careful with what we were doing, but I can assure that our "parts" or whatever NEVER physically came in contact.

But now since I haven't gotten my period for this month, I keep replaying the incident over in my head, scared that maybe I overlooked a detail, and something might have happened that gotten me pregnant. There really is no other reason for my period being late unless it is just a fluke? I'm not that stressed or anything (well NOW I am just thinking about my situation)...

I don't know what to do... I always thought I was smarter than this, but I guess I'm not and now I deserve it.