Alli weight loss pills and missed period?

This is an odd questions, but Im curious if anyone else has experienced this.... I started taking the Alli weight loss pills about two weeks ago. I have not had my period this month (I'd say Im about a week late now) and am a little concerned. I took a pregnancy test, but it came back negative. I cannot figure out why I would not have my period and the only thing I can attribute it to would possibly be the Alli weight loss pills. Have any other women had this problem? Or, does anyone know if this may be a side effect of the pills?? Please help!