Not sure if im pregnant?

My period will be a week late tomorrow. According to the calendar I'll be 5 weeks pregnant tomorrow. I took a pregnancy test yesterday but it was negative and not my first pee of the day. I'm cramping and keep thinking that my period is coming on but its still not here. Lately I've been having mild pinching cramps on the left side of my abdomen. Did anybody ever go through the same thing I'm going through now. I have been taking prenatal vitamins but I'm not sure IF that can delay my period. Any suggestions?