Welcome to Healthcaremagic,
Thanks for posting your query,
First please understand very clearly plan B tablet should not be used as regular contraceptive
method even if you are having sex only twice a month.
This pill if taken before ovulation produces withdrawal bleeding and if it is taken after ovulation in luteal phase then it can delay the period so you have delay of >10 days.
You should take a urine pregnancy
test if the test is negative you can wait for few days but it is better to consult Gynecologist to get Beta HCG
of abdomen as some times tubal pregnancy occurs which if ruptures in a kind of emergency.
Please be in touch with Gynecologist as soon as possible.
Once this is resolved please practice safe sex and use some regular contraceptive methods there are so many options available, remember barrier methods
not only prevent unwanted pregnancies but also protects against sexually transmitted diseases.
Please take good care.
Dr.Akhilesh Dubey M.D.