You should take balance diet which includes all vegetables .fruits .pulses. Meat and specially milk. These food substances contain all the necessary nutrients which will make you energetic and healthy ............ !
try eating a lot of food that will give you energy like milk,milkshakes,and lots of protein also food that will fill you up. If u start doing this your body is going to start gaining weight and your not going to be skinny anymore.
shakiness and low energy could be simply low iron or protein... or something more serious that requires medication. My ex-wife would shake and suffer low energy then pop an iron pill and be good for 2 months. My cousin had the same symptoms and required medication. Sorry, you really should see a doctor and get some blood tests done.
Gaining fat and gaining fat and gaining muscle are two different projects. To gain fat - don't exercise and eat junk food -= especially fast food. Lots of sugar, carbs, bread, pasta, potatoes, and rice. Muscle - work out, eat protein. You may lose weight at first, working out burns fat, but then you will stabilize and gain as muscle replaces fat.
Whatever you do I highly suggest seeing a doctor and take supplements like a multi-vitamin daily.