What are my chances of pregnancy??

I take my pill almost perfectly give or take a few minutes but I haven't missed one. My boyfriend and I had sex about 3 or 4 weeks ago (he never comes close to finishing inside me) and for about 2 weeks now I've been having cramps in my lower back, upper thighs, and lower pelvic region. My boobs look kind of veiny and might be a little swollen but I'm not sure. My period is due in 2 days but these symptoms have been going on for a little while. What are my chances of being pregnant?? I've been so paranoid and stressing like crazy!