I missed a period due to stress, then had sex and the condom broke, took plan b & got my period 2 weeks later. when should my cycle go back to normal?

1-3 Months: Give it some time, maybe 1-3 months to 're-normalize'.

Plan b: Can affect cycles for up to 2to3 months. If you are sexually active, you should consider better birth control such as the pill, or an IUD if you are not looking to get pregnant.

"plan B": period ?: Your period after using "plan B" should be a normal one, and your cycle should resume at the usual interval as prior to the events described in your question, i.e., within a month or so. Your cycle may be a little delayed if ovulation is delayed due to the actions of "plan B", so if your period was not of normal duration, and five weeks pass, get a serum pregnancy test.