What Causes Delay In Periods?

Hello.. I know that this problem is probably more suitable for a gynecologist, but I really need an urgent advice. More than two months ago, exactly on the 22nd of April I took a morning after pill. Later on the 5th of May I got my period. However this month (June) I haven't got my period and I am starting to get worried. I took a pregnancy test few days ago and it was negative. And I haven't got any of the other early pregnancy symptoms other than the fact that my period is late (or I am missing it by one month). What else can I do? Is there a chance for me to be pregnant?