My period is late. Last intercourse 5 weeks ago was protected, I had a heavy period the week after and three negative tests today. Very confused!

Tests are accurate. Home pregnancy tests are very accurate and not affected by foods, herbs, common illnesses, sexually transmitted diseases, or medications. A correctly done urine test gives a reliable result 3 weeks after sex (3 weeks after when conception might have happened) or 1 week after missing a period. If done sooner, a positive result is likely real, but a negative result may be due to testing too soon.