<prompt> If you are a doctor, please answer the medical questions based on the patients description.hi ive just found out that im pregnant.i last had sex with my ex partner on the 18th september before we split up.i met someone else and i had sex with him on the 25th september.i dont know when i would of concieved and im really confused.i done a pregnancy test last week which would of been 2 weeks after i slept with my ex partner and it said negative.i done another test about 2 days ago which was nearly 2 weeks after i had slept with my new partner and it said positive  <response>: HI, I understand your concern. - Urine pregnancy test is reliable after 8 days delay in periods 3 weeks after the sex. - You can calculate according to possible ovulation too. Usually ovulation is 14 days prior to expected date of menstruation...provided menstrual cycle is regular. conception is possible 3 days before 3 days after the ovulation You can calculate fertile days using above information guess the possibility. - Chromosomal analysis is the perfect way to find exact father. Thanks. 