How Safe Is Taking Duphston To Extend The Menstrual Cycle?

My period date was 28th Dec 2011.. My doctor had prescribed me Duphston from 23th Jan 2012 to extend my period date & he told if u r pregnant it will help u .. but today 27th Jan 2012, it started to bleed a bit ..Y it is so ? & Y it didnt extend ?? Please help .... & Im taking preganacy treatment from last 3 years,, MY HSG is done, it is normal, but my hubby has low sperm count i.e 10 million.. & his treatment is going on ... Pls advice