Whey protein drinks and gaining weight?

I am going through a divorce and very stressed. I don't have much of an appetite so I eat a light lunch and enough to get full during supper. I normally weigh 98lbs and look decent because I am short but now I am just bones (probably early 90s). I'm trying to gain weight and I am not very active. The drink mix I got is 26g of protein and 140 calories. How much should I drink a day and when? And will it help?