I had unprotected sex and 3 days later i took the plan b and last time i took it which was the first time i had symptoms but this time i'm not having ?

Symptoms vary: The timing in terms of where you are in your cycle and how long after intercourse as well as anything else you may be taking will all influence what if any symptoms you experience. Plan B is better than nothing but is not really effective birth control, 3 days is really pushing the limit, and if you continue to rely on it you will probably get pregnant.