I had sex 5 days ago and it was my ovulation day! Today I'm feeling nipples pain! Is it a sign of pregnancy?

Too soon. Sex 5 days ago, if successful in conceiving, would mean conception 4 days ago... which is too early to CAUSE any symptoms. That means any symptoms one feels would be unrelated to pregnancy, or would be related to a pregnancy that started longer than a couple of weeks ago. A home urine pregnancy test is very accurate, abut 3 weeks after sex.