What is wrong with my stomach? I've had this for MONTHS!?

So, It started off having reallly intense stomach pain and throwing up. I was rushed to the hospital twice because of it. Now it is happening more often. No matter what I eat, or drink, or do I get sick. It is like food poisening but about 10 times worse. Now it happened again today. It starts with my stomach just being upset. Then pretty soon it feels like my stomach is lurching then I get sick. Sometimes it comes with extreme dizziness and headaches and shakes, sometimes it doesn't. It comes in waves also. I will fell very sick one minute and the next I feel fine. The doctors have taken ultra-sounds of my stomach, upper GI's and many many other GI tests. They can not find anything. Some days I won't eat any thing at all and I still get sick. What could be wrong??