Hi, Welcome to HCM, In a regular menstrual cycle of 28 days, ovulation generally occurs on the 14th day of menstrual period. One can become pregnant due to intercourse, on or around the day of ovulation. Thus you could be pregnant, if you had unprotected sex around expected date of ovulation. Urine test for pregnancy is not very sensitive. Ideally, you should get blood test for pregnancy done. In a women of child bearing age, the most common cause of abnormal uterine bleeding is pregnancy and its complications like ectopic pregnancy and miscarriage. Other causes are hormonal imbalance, trauma, anovulatory cycle, infection(cervicitis, endometritis, vaginitis), uterine polyp/fibroid, P.I.D., cancer (of vagina, cervix, uterus, ovaries), certain drugs and bleeding disorder etc. Detailed history, examination and investigations are required. Thus you should consult a Gynecologist to establish a diagnosis and treatment. Thanks for trusting Healthcaremagic and posting your query. Hope you found my response to your query informative and helpful. If you have further concerns in this regard, you can submit those with Healthcaremagic as well. With good wishes,