Tested negative 4 weeks after sex. now light pink when i wiped yesterday cramping & back pain 2day/yesterday can implantation happen 4 week after sex?

No: 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.