Please help

I had sex one day and 5-6 days later I went to bay clinic to take a pregnancy test. It came out negitive but the doc said it was still early to tell if I really em. She gave me plan B and gave me birth control so I could start taking it the vet next day. It's been almost 3 weeks and ever since then I've been feeling dizzy, always having that feeling to throw up and hungry a lot. My boobs are so sensitive and I'm so moody I don't even know why I'm mad most of the time. My boyfriend thinks I em pregnant. And just hearing him say those words made me scared. I wanted to see what your opinionsare about this.