I'm on tri previfem (norgestimate and ethinyl estradiol) and took plan b 3 weeks ago. i have a yeast infection w/blood. is the blood from plan b or is it a sign of implantation? nervous

Confusing: If you are already on birth control pills then there is no need to take Plan B as you were already protected. Implantation bleeding only occurs if you are pregnant which is not likely since you are on birth control. Yeast does not usually cause blood. I suspect you just triggered some bleeding from adding Plan B on top of your birth control.