Nausea early pregnancy?

Hi there. My husband and I have been trying for a baby and I was just wondering if I could be pregnant, and if anyone else has experienced this. Yesterday I had my usual coffee for lunch at work, and a bit later I was sitting at my desk feeling like I was about to vomit. About an hour later it went away. Later that afternoon, it came back and I'm still experiencing it, but it only really comes on when I eat. I also feel like I'm full quickly, then i'm hungry again. I took a pregnancy test before and it was negative. It wasn't my morning wee, but surely if i am pregnant enough to cause nausea, wouldn't i have even a faint line on the test? I have no other pregnancy symptom. I feel a bit crampy down there like i get a twinge every now and then or feel briefly like i'm getting a period. Just wondering if anyone else experienced this and had nausea before a positive test. Thanks so much.