Could The Diet Pill Hydroxycut Have Delayed My Periods?

I started taking Hydroxycut last month (June 2010) and have taking them regularly. My period was due on July 21 but I have not bled at all. I did have unprotected sex a week before my period was due (July 14) but I have not experienced any early pregnancy symptoms. Could the diet pills have a cause to my missed period? Or do I need to take a pregnancy test?