From what I understand, Plan B can cause spotting to occur and it will be normal. Brown discharge also isn't exactly abnormal for any woman and doesn't always mean pregnancy. The only way to know for sure is with a test. Keep in mind the pull out method is not protection against pregnancy. Plan B is a very heavy dose of hormonal birth control, which can have some serious side effects- especially if you use it regular, so be careful with that as well.
What was your steroid shot and other medication for, and what types? Are you worried it may have effected a possible pregnancy?