Can Plan B work after giving birth a month later?

Plan B works. Plan b works when taking as soon as possible after unprotected intercourse. If you gave birth one month ago then you may have ovulated and pregnancy is possible. It is most effective when taken within 72 hours of intercourse.
Plan B. Agree with Dr. Livingston. Plan B can be used even if you are post-partum. Plan B One-Step can reduce your risk of pregnancy by up to 95% if used within 24 hours of sex. If taken within 72 hours it can reduce risk of pregnancy by up to 89%. .