Am I pregnant?...

Stephanie • Hi
So I usually have a 5-7 day period but this time I only had my period for 2 days. It was light for the first day and very heavy the second like my period usually is ... But then it stopped abruptly. 
A couple days ago I started randomly getting nauseous and puking and it would just go away. I haven't changed my diet and I'm not taking oral contraceptives or anything so my estrogen should be the same. My breasts have also been sore. I felt as if I was pregnant before my period came and took 3 pregnancy tests and they all came back negative. 
Should I go out and buy another one? Did I test too early? Is something else going on? I'm so confused! I feel like because of the negative tests and bleeding I shouldn't be pregnant but I'm having a lot of symptoms at the same time ..