Hi Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concern.
Yes intake of plan B can cause brown vaginal bleeding &
abdominal pain. The bleeding you had must be
breakthrough bleeding. This type of bleeding normally occurs within 3 weeks of intake of a plan B pill or
emergency contraceptive pill.Actually a plan B pill contains high dose of levonorgestrol hormone, which disrupts your
normal menstruation cycle & causes this bleeding. There is nothing much to be concerned about it. You could also have your next period delayed.
Abdominal pain or cramps you had are common side effect of the pill. You could take normal painkiler like ibuprofen/acetaminophen for that.
Don't use a Plan B pill too frequently. Use condom or regular contraceptive pill as method of contraception in future. Regular taking emergency contraceptive pills can cause problems like
irregular periods, ovarian hyper-stimulation syndrome & even infertility.
For more queries consult a gynaecologist
Hope this information helps