I Have Been Nauseous For About 3 Days Now. Slight

I have been nauseous for about 3 days now. Slight headache as well. My girlfriend also mentioned that she felt sick to the stomach. I haven't thrown up but certain smells are making me feel like I want to throw up and I am not one to get sick to smells like that. I don't know what's wrong but my doctor that I work with prescribed me Zofran. I've only taken one since but I would like an answer if anyone can answer what's causing this nausea. Thank