I took a pregnancy test(negative) but i have been in a state of nausea for about 3 weeks not every often, but all day long. what could be wrong?

Check it again : You should take a pregnancy test again now. When the pregnancy is at a very early stage, the b-hcg level is still very low and undetectable which will give you false negative pregnancy test. Take the test again now to confirm. If negative again, you should go to see your md and have yourself checked. Other condition such as gastritis, stomach ulcers, other GI problems etc can cause nausea

Blood test for HCG: If you have any doubt, get a blood test for HCG level to settle the pregnancy issue.