period late 19 days, negative results.

my period is 19 DAYS LATE!!! i keep testing at home, i took one every week since i’ve been late but they’re all negative and i have no symptoms. any ideas why this might be happening? i’ve also been having sharp pains in my lower abdomen, and thought i was having pms, and then never got my period.

also update to the first comment: i’m 20, so it’s definitely not menopause, and my stress levels have been actually lower than normal lately.