Missing period 19days late no sex

Meca

It’s been 19 days since I last had a period . I have had no known sex in the past month but have been taking some medications such as antibiotics which My dentist says does not affect your period . So what could it be . I’m never this lady’s even when I stress. It’s possible that a man has been with me while I sleep (my estranged husband ) but that’s neither here nor there . When should I take a pregnancy test ?