Help please!!! I'm so confused! OMG

I woke up this morning (30th) and had 3 urine home pregnancy test done and they are all positive. My period was suppose to come on 29th and it didn't. I got suspicious. I have 2 major CAT scans do do tomorrow and now this. Before my doc ordered them I had a pregnancy blood test done on the 17th that was negative! What should I do next? What's going on? I had my period cramps but so far no period!