As your period cycle is regular (exact 28 days), then you need not to take additional Progesterone
One time delayed period (4 days) is not clinically significant until persistent irregular or delaying. Also pregnancy
test is negative.
Delayed period has several causes with exclusion of pregnancy like emotional upset, stress, anxiety
problem, PCOD with Over weight. So need to investigate properly.
So better to wait at least 7 days and if you not get your period,consult with your gynecologist. Don't take medicine without doctor prescription.