What Causes Nausea With Negative Pregnancy Test?

i am experiencing nausea for the last week and a half. its not paired with any other symptoms. it is during random times of day, sometimes morning, sometimes evening. i took a pregnancy test and it came out negative, but i'm not due to have my period for another week. is there a way that i can be this nausious due to preganancy, but the test couldnt detect it?