Body vitamins. Feeling lazy. End.

Hi , I have been feeling lazy and and lethargic of late , since about a year . I'm not able to focus on work and get distracted easily . Since I work in IT , my diet mostly comprises of staple foods from food courts and house cook with routine foods. I have lost weight and I look lean instead of fit (which I was a year ago) and I feel unmotivated. I run out of energy really quick and lost stamina. I feel my body is lacking vitamins (probably of all kinds) and looking for advice on how to get back my body to healthy state. Are there any consumables of multivitamins which I could use so as to get better and also improve my memory and cognitive skills . Correct  me if these are just placebos During this covid-19 lockdown . How can I get better staying at home so I return back healthy and sound when these restrictions end. Thank you for your suggestions and answers.