What's going on with my body?

Okay so I was supposed to start my period the 2nd now it's the 11th and still nothing. I took two home pregnancy tests and they both came out negative. The last week and a half i've been nauseous around 2 am and until noon and sometimes when I eat I throw it up. I can defiantly be pregnant, but they both came out negative and i took them separately on two different days. I've been eating pretty healthy and excising regularly, not excessively. Does anyone know what could be up? Please and Thank You.