What can happen if you take plan b have a period 2 days later (about 2 weeks early) then after that period have to take it again ?

Once should be : Enough. Please use oc's or condoms in the future.

It can cause side: effects. Potential side effects w emergency contraception includes menstrual flow changes (spotting, bleeding, early or late period), nausea, vomiting, dizziness, fatigue, headache, breast tenderness & abdominal pain or cramps. Take pregnancy test & notify dr if your period is 7 or > days late. You need a regular form of birth control.