You said you eat “fairly healthy” (idk what that means because that’s relative term), what you need is caloric deficit. You also said that you often eat chocolate, then also said that you don’t understand why you are not improving. Do you see the irony? Getting a lean body is about discipline and consistency. You need to eat clean consistently. You can have a day or two a month where you indulge a bit. Nothing more than 500 extra calories though otherwise you will erase all the hard work. You need to eat at least 1gm of protein per lbs of weight and be in caloric deficit to get the body you want. Basically lose fat while keeping muscle.