Need help??

Me and my boyfriend had sex unprotected sex on a day my app.said it was my ovulation day. Three days later i started spotting when my period was due in a week. A week later i didny see my period and my period always on time and regular. Lately i been having mild cramps,nauseous,lil headaches,tired and bloated. Some days o thought my period was coming but it never showed. I took a pregnancy test at night and it say negative. I was in formes by friends that sometimes it say negative and you can still be pregnant. Also sometimes its best to take a pregnancy test in the am. Im waiting till this month is up to see if my period will show up or not. I need opinions and help.also i want to know uf anybody else experiencing this and what should i do?