Definitely use a form of birth control as taking plan b so many times in one month is not optimal. It will most likely cause titu to not have a period after taking it especially since you took 2 doses. If you miss your next period I'd definitely take a test but its pretty effective if taken within 72 hours
It is hard to say, as plan.b, the morning after pill we call it in uk, will mess up your cycle and hormone levels. also you took it twice in your cycle. So being able to pinpoint your most fertile days would.be impossible. Best thing would be to wait until your expected period due day and try a test. If it is negative test again once each week until either your period comes or a positive. Good luck x