Confused

Okay, last time I posted I asked about being pregnant and it not show. Well its been about a week, I'm still nauseated, and etc.. But I'm not sick, all pregnancy test have came back negative. My doctor still thinks I'm pregnant. But won't do a ultrasound to see. My next cycle is next week. Doe's anyone know what could be going on, or what I could do? Because I'm stressing out over this.