Doxycycline hylclate: could I be pregnant?

I went to the hospital yesterday and the doctor prescribed me doxycycline for bronchitis. I took the pill and it made me vomit. Everytime I try to eat I feel nausiated. All I can do is drink fluids. I didn't eat all day yesterday and I haven't eaten today. I ate half of a saltine cracker a few minutes ago but it made me feel sick. I ask of I'm pregnant because when my sister found out she was pregnant she had taken an antibiotic like what I'm taking and she couldn't eat because she would throw up everytime she tried. Her and my mother are convinced that I'm pregnant. Has this ever happened to anyone else? I don't weigh much so I need to eat but I get sick everytime I try. Someone please help me. I feel so sick..... Please... I need answers.....