Hello! Oral contraceptive pills and hormonal contraceptives are very commonly associated with various side effects like delayed period, irregular cycles, unexplained intermenstrual bleeding or spotting, lower abdominal cramps, nausea, etc. Since you had irregular periods in the past as well, it is difficult to say the exact reason for the delay in period. However, since there was an episode of unprotected intercourse, I would suggest you to take a urine pregnancy test with an early morning sample of urine to exclude the chances of pregnancy. Applying heat pads over the lower abdomen, taking a hot shower, gentle massage over the lower andomen, drinking plenty of water , warm water with sugar are all known to help ease cramps. OTC pain meds like acetaminophen or ibuprofen can also be tried for temporary relief. Please get back in case of further queries :)