What Causes Delays In Menstruation?

Hi, I had a normal period in Jan always regular heavy flow lasting 5 to 7 days. February I had a blob of white stuff milky colur and stretchy with a very very light period lasting two days. Now march and no period I have been getting cramps as if I am getting period but no sign also have bloated lower tummy feeling very strange. Negative pregnancy test what could this be. I am over a week late now.