4 weeks ago after unprot sex, i took plan b, got period next day, after 4 weeks i had 4 neg tests. my boobs have been hurting. my period isindue8days.

Likely not pregnant: The tests are quite reliable starting 2-3 wks after exposure when a pregnancy is present. If you miss your next cycle you can test again to be sure, otherwise I would accept the test results. Boobs hurting from a pregnancy would only occur if the chemicals made by the conception were there & these are what turns a urine test positive.