Kind Sir,
I have read the problem you posted. Medicine cannot be suggested as there is no health history. What disease do you have that is causing this weight loss? What medications are you currently taking? Is your appetite the problem, you just don't want to eat? What, sir, do you want treated? Weight gain (just like weight loss) does not come in a pill.
Here is what I want you to do. Eat a substantial breakfast, lunch and supper with two snacks in between. Make a high calorie protein shake to take at least once per day for added weight gain and vitamins. It can be as simple as adding a breakfast drink packet into milk or milk substitute. If you have a blender put it in the blender with fresh or canned fruit and blend. If you want it thicker, blend with ice cubes.
Add avocodos liberally to your diet. Make your own dressings from virgin olive oil and use for dipping or salad dressings and use liberally. Kindly get your health back.
Let me know in a few weeks how you are feeling. KathrynShattler,MS,RDN