Hi,
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Emergency contraceptives work if taken within 72 hours of the unprotected intercourse. The regular birth control pills too give you protection after you finish 1 pack and start with the next (with having a period in between). Since you were off the contraceptive pills for 6 months, the continued protection will not be there, it will be like starting a new birth control altogether.
The cramps that you are having could either be due to pregnancy and possible reaction of uterus to implantation or due to probable indication of impending withdrawal bleeding due to emergency contraceptive use (they contain high doses of hormones).
Visit your gynecologist for a thorough check if you do not get your periods and suspect pregnancy. A blood beta HCG test will help to confirm/rule out pregnancy accurately as early as 11 days post conception. Request for getting this test done.
Take care.