Starting to worry

My period was suppose to start on the 18th but it didn't start until the 22nd but for about three weeks now I have been really dizzy and lightheaded coupled with nausea and the pass couple of days I have been having lower abdominal cramping. I have taken 2 pregnancy test and both were negative. When I told my aunt about the first thing she said was that I could be pregnant. Not sure what to do.