Suggest Dosage Of Postinor-2 To Avoid Pregnancy

hi ,i have a question regarding prostino 2 and pregnancy. some times i have to take 2 or 3 prostino pills after having sexual within 2 weeks.Is that good for my health? what is the probability of getting pregnant if i get late to take the second pill of the prostion package.often i get late 2-3 hours from 12 hours before the first taking.