Pregnant ?

My periods are regular. So every 27 or 28 days it comes on. Sometimes a little earlier. Now I was fertile from the January 2-6 I had sex on the 2,3,and 5th. On 12dpo my nipples got really sore. My period suppose to come on Sunday January 19. It doesn't feel like it's coming on at all. Today is Saturday the 18 my nipples are still sore. I took a save a lot brand pregnancy test yesterday. It can back negative. I'm just wondering can I still be pregnant or is if all in my head ?