Astigmatism is very, very common. What it is....the rounded surface of the cornea becomes slightly pointed. It can be corrected with glasses, or toric contact lenses. I believe, in more severe cases, laser surgery can now be used to reshape the cornea.
You didn't say how serious your astigmatism is. Generally, it shouldn't cause headaches and nausea, unless you are in really bad need of glasses. It sounds more like migraine headaches to me.
Hope this helps.