i thought that plan b would cause a period?

Hi,
Welcome to ehealthforum,
Stress and use of emergency contraceptive pills, both can delay your periods. If you have taken the emergency contraceptive pills within 48-72 hours of the unprotected sexual intercourse as per the given instructions, it should work in preventing pregnancy (provided you were not sexually active without protection after taking it). Withdrawal bleeding usually occurs within 5-7 days of taking the emergency contraceptive indicating that the pill has worked (which might not occur if the pill is taken close to your period time). Since the emergency contraceptives contain high doses of hormones, these can disrupt the normal hormonal and period pattern causing period/bleeding abnormalities. Wait and watch for your next periods which can be delayed. Look out for development of any other new symptoms if pregnancy is suspected. If pregnancy is suspected, or if you miss your periods, or if you have abnormal periods, consider visiting your doctor/gynecologist at the earliest for thorough examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately).
If pregnancy gets ruled out, and if you are not ready for pregnancy, but intend to remain sexually active, you should consider visiting your gynecologist to get started on suitable regular birth control measures to be protected (after your periods). Be regular with birth control use as instructed. Avoid having unprotected sexual contact. Be in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately. Drink plenty of water. Take adequate rest. Maintain healthy diet and lifestyle.
Take care.