Is it normal to have light dark bleeding with chunks of dead tissue for more than a week long after taking plan b?

This is not normal: It is typical to have a menstrual period after taking Plan B as prescribed (within 72 hours of having unprotected sex). The chunks are likely to be an organized blood clot, which is often described as tissue-like. You need to exclude pregnancy, particularly if you took the Plan B later than 72 hours. Once excluded, you may start or restart new contraception.