Is it okay to masturbate after unprotected sex and taking the plan b ?

Yes: Plan B is called B because it is a back-up emergency plan. One does not use Plan B as her Plan A. Instead, one should avoid having sex until a good Plan A is in place... with the goal of never needing Plan B again. Plan B is not to be used as one's method of birth control. Plan B is an emergency back-up plan, so should be used no more than one, two, or three times in an entire lifetime.