Which medication can i use to prevent pregnancy past 3 days of unprotected sex after the periods?

On days 4-5?: If on days 4-5, there is no time to waste. If pregnancy is possible, a primary care doctor may prescribe Ella, (ulipristal) which should still work on days 4-5. Plan B may not work as well as Ella on days 4-5. Another good plan is an IUD, which can be placed by an Ob-Gyn doctor. An IUD prevents pregnancy and starts working now (plus avoids the need for future Plan B or Ella). Always plan ahead.