What could be causing these symptoms?

I have been experiencing these symptoms for about a year. I feel vibrations throughout my whole body; it feels like something pulsing or beating inside me, similar to a heartbeat. I can feel it all day, but it becomes more noticeable when I lie down. The shakiness is sometimes visible from the outside. When I clench my hands or make a fist, I can feel the vibrations in my fingers and toes. I constantly feel the need to lie down or have my back supported; otherwise, I feel a kind of light-headedness. When I lie on my left side, the internal tremors become much more noticeable compared to the right side. In addition to this, I experience frequent burping—sometimes excessive and sometimes less. I have undergone many tests, including blood work, CT scans of my head and neck, ECG of the heart, and a chest X-ray, but doctors have been unable to identify exactly what is causing these symptoms. This makes me feel very distressed and worried. These symptoms are affecting my daily life, and I constantly fear that something awful might happen. I goto doctors regularly but they are unable to find what's going on. I truly don’t understand what is going on and would really appreciate help.