Late period

So my last period was the 10th june and my cycle is around 30-34 days long usually, it said i would ovulate around the 29th/30th and at that time i did get egg white mucus, however i am now 5 days late and 2 days ago i took a pregnancy test and it was negative, i have also for the past week been experiencing very dull like cramp feelings in my lower belly. why could my period be late ? I haven’t been more stressed or anything so im abit confused on why i haven’t started yet ?