What Causes Menstrual Delays With Breast Soreness And Stomach Bloating?

Hello-I am a healthy 27-year old female and am currently 13 days late for my period (last was on April 28th 2011). As my birth control we use condoms and the withdrawal method. The last time I had sexual intercourse with my boyfriend he never ejaculated in my vagina so I highly doubt I'm pregnant. However, I plan on taking an at-home pregnancy test tomorrow morning to be sure. I've been pregnant before, but the cause was a broken condom. My menstrual cycle is usually irregular (usually 2-5 days late monthly), but it's never been this late. My breasts are sore and I feel bloaded but I've had these same symptoms for 13 days and understand they can be premenstrual symptoms as well. Very concerned--if I'm not pregnant, what else can cause this lateness?