Can anyone please help me ?

Did you read this thread?

http://community.myfitnesspal.com/en/discussion/10326769/are-you-a-hard-gainer-please-read#latest

There's a whole list of calorie-dense foods in there, quite a few of which also deliver some decent nutrition, not just calories.

Also, for shakes, consider protein powders marketed specifically as "mass gainers". (Read labels carefully; some supplement sellers sell junk.)

While ultra-high calorie meals/shakes will help to gain weight quickly, usually a (very) high percentage of that weight is bodyfat, not muscle. If that's what your doctor wants, go for it. If, however, your goal is to gain muscle, then the eating goal should be high protein and the day's total only slightly over maintenance, say 250-500 calories over the calorie total which keeps your weight constant. Gain slow, much of it can be muscle; gain fast, much of it will be fat, which then has to be dieted away to reveal whatever muscle came along for the ride.