I took Plan B the day after my period ended. I started bleeding 6 days after. The bleeding has not stopped, but fluctuates in amount. Concerns?

Not certain. Potential side effects w emergency contraception includes menstrual flow changes (spotting, bleeding, early or late period). If you have significant bleeding > 7 days or you have hemorraging - that would be of concern. This may be a Plan B side effect.
No concern. Very common period mess up by plan B That's why not good to use it frequent.