Sex/not pregnant not understanding

Okay so I had protected sex for the first time 5 weeks ago. Missed my period 2 days ago. I took a pregnancy test yesterday. It came back negative. Went to the doctor they said if your not showing pregnancy sign and the pregnancy test was negative then you'll be fine. I'm sick atm and was under a lot of stress. Still having cramps and not feeling well. So I don't understand why I haven't had my period. Also I threw up yellow bile this morning. Any ideas?