Am I pregnant? Please help.?

I had unprotected about 3 days ago, and though I'm sure my boyfriend pulled out before he d, I'm worried. My period was supposed to be yesterday, but I missed it. This is completely normal for me. I have never had a regular period in my life since I'm so under-weight and usually always stressed. It can even be weeks late sometimes, so that doesn't help to answer my question. Although, my abdominal area is sore, and my WERE sore (now they're not much anymore though), and I don't know if this is in my head because I'm so worried, but I've been lightheaded. Although, I haven't been nauseous, I've actually been very hungry. These are symptoms of pregnancy, but also symptoms I get before I get my period. Should I worry? Or get a test? I'm really scared. And if anybody can TRULY help, what are some OBVIOUS symptoms of EARLY pregnancy that differ from an impending period?