Missed period on clomid

Has any missed a period whilst on clomid and the pregnancy test is negative? My last period was the 9th December 2015 n I took clomid 50mg frm day 2-6 n I still haven't got my period. I took a test yesterday and it was negative. The first two rounds my periods were on time n this was my last round n still no period....has this happened to anyone before?