Pregnancy??? Help please!

So me and my boyfriend had sex on the 20th and he didn't pee after ejaculation the first time he pulled out before cuming the second time. We didn't use a condom either times . I didn't take plan B. It was on one of tmr fertile days too. I don't take birth control and stuff. I experienced lower back pain once or twice but that's pretty much it and I took a urine pregnancy test on the 30th. I haven't experience any symptoms of pregnancy though. Could I still be pregnant? The test said I was not pregnant. Could I still be? My period is very irregular. What do I do?? I've been extremely stressed about this. Please help.