While you're trying to figure this out, and you do need to see your doctor for this, if you aren't sensitive to ginger, try making some ginger root tea. It's inexpensive and it's easy to do:
In a small saucepan (about 1 qt) fill with water and bring to a boil. Meanwhile, peel and slice a one to two inch piece of ginger root. Add to water. When water comes to a rolling boil, turn the heat down to a medium high heat and cook 'til half of the water has evaporated. It really doesn't take as long as it sounds like it would.
I agree that many things can cause such nausea. I have problems with nausea. I'm still waiting for some test results myself. But, I already had some diagnosed problems that will cause nausea, such as IBS and GERD.
Hi nausea is such a vague symptom so it could be hudreds of things. I would suggest a visit to the dr to get things checked. He would probaly start with simple blood tests and if needed refer you to a gastro doctor who could do more tests to find the cause.