If your are late by 16 days and still the pregnancy tests are negative then it is unlikely that you have become pregnant in this cycle.
It is advisable that you may visit your physician for an ultrasound to check for endometrial thickness.
If its more than 10mm, then you may opt for a withdrawal bleed with progesterones to resume your menses or if even this fails then a possible dilatation and curettage may be performed for removal of this cycle's endometrium to allow a fresh cycle to resume.
I hope I have answered your query in detail.
It is suggested that you may opt to use ovulation kits to time your ovulation and plan timed intercourse accordingly.
Wishing you good health,
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.