How long before pregnancy test?

I had sex on the 19th, 24th, and 27th of april all using widthdrawl. My boyfriend spilled sperm on top of me. One day before my period started..I moved and some fell down my vag...i cleaned it right away but days later i felt nausea.. It soon became a problem because I had very bad nausea in the mornings and at times throughout the day. My period came normal and actually pretty heavy...my concern is the symptoms i have been experiencing..I get bad headaches,dizzy and nausea. I ve been geting very hungry many more times a day...Should I take a test its 8 days before my next predicted period. i took a test after the 19 th and it was negative. i figured that if i got my period on time after having unprotected sex it would mean i was not pregnant... Is it too early for implatation to take place. Any advice.