Hi Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concern...
Yes, Intake of a plan B pill can cause brown
vaginal discharge. The Discharge or bleeding you had must be
breakthrough bleeding which normally occurs within 3 weeks of intake of a plan B pill. This is normal feature of intake of Plan B pill & you should not be much concerned about it.
This bleeding is due to high dose of
levonorgestrel in a plan B pill, which disrupts your normal menstrual cycle & cause this type of bleeding. Breakthrough bleeding most probably means that intake of Unwanted 72 was successful in preventing pregnancy.
Don't take a plan B pill too frequently. These pill can cause
irregular periods & other serious side effects. Use condom or regular
contraceptive pill regularly as method of contraception in future. Also withdrawal of penis before ejaculation & wiping the penis after ejaculation does not rule-out pregnancy completely. Therefore you should avoid these in future.
Refer to a gynaecologist for more queries
Don't worry you would be fine
Hope this information helps