My last period was march 17 . i had unprotected sex on the 5 of march and used plan b. 16 days late on my period and sore breast negative pregnant test ?

May need to test: Although emergency contraceptives like Plan B prevents about 74% of pregnancies, there is still the chance you could have become pregnant. It's hopeful that you did have a period following the planb (was it a normal period?) but it's possible you could still be pregnant or your body is just adjusting to the large dose of progestin from the planb. See your doctor for testing if more than 21 d past.