How Can Dizziness And Lightheadedness Be Treated?

I have had dizziness and lightheadness for almost two years now and my doctor, gastrologist, neurosurgeon, neurologist, ear, nose & throat doctor, took MRI, CT scans, and exrays, plus the procedure of having a camera down my throat for 24 hours AND had blood work done. No one can tell me why I am dizzy. I happens most when I eat food or sometimes drink. Any suggestions? I do have GERD and dyspepsia. Prior to all this, I did have a procedure done on my left shoulder, and was taking meds, immediately after this procedure is when the constant dizziness began. Thank you for your knowledge and time