I'm 16 days late,been pmsing strongly but no tender breast or cramps. tested -ve 4 times. could i still be pregnant but hcg levels not strong enough?

Unlikely: One can do 1 more test after another week passes. Home pregnancy tests are very accurate and not affected by foods, herbs, common illnesses, sexually transmitted diseases, vaginal spotting, or medications. A test gives a reliable result 3 weeks after sex or 1 week after missing a period. If done sooner, a negative result may be due to testing too early such as less than 2 weeks after conception.