Hi It is not easy to predict the exact day of Ovulation.The time from the beginning of the last menstrual period (LMP) until ovulation is, on average, 14.6 days, but with substantial variation both between women and between cycles in any single woman, with an overall 95% prediction interval of 8.2 to 20.5 days. Cycle length alone is not a reliable indicator of the day of ovulation. While in general an earlier ovulation will result in a shorter menstrual cycle, and vice versa, the post-ovulatory phase of the menstrual cycle may vary by up to a week between women. The symptoms MAY be due to pregnancy. Most chemical tests for pregnancy look for the presence of the beta subunit of hCG or human chorionic gonadotropin in the blood or urine. hCG can be detected in urine or blood after implantation, which occurs six to twelve days after fertilization. Quantitative blood (serum beta) tests can detect hCG levels as low as 1 mIU/mL, while urine test strips have published detection thresholds of 10 mIU/mL to 100 mIU/mL, depending on the brand. As 12 days have been completed after your intercourse,Pregnancy test can be done by simple Urine test strip with the advice of your doctor. If it is negative,then the other causes have to be looked for. Wish you good health.