I had unprotected sex on january 25 & 26th my ovulation day was on the 26th of january. my period was 3 days late, i was spotting between my period and it last longer than usual. could it be a sign of pregnancy or std?

Hard to guess: For fertile women who are having sex... it can be hard to tell if a woman is pregnant because some of the symptoms seen in early pregnancy can also happen in non-pregnant women. A home urine pregnancy test gives a accurate result. One can test about 3 weeks after sex (3 weeks after when conception might have occurred), 1 week after missing a period, or 1 week after starting a "weird" period.