Ice Cream and Milkshakes will pack some weight on if eaten before bed, but they come with alot of sugar. You may want to head to a health food store and ask about a Weight Gainer Protien Shake or Liquid Meal Replacement like Ensure, Slim Fast etc. If you eat normal meals each day and add a Slim Fast drink you will gain some weight as you are adding more calories.
You can also download NOOM App for free or go to My Fitness Pal online and use thier calorie counters to track your food caloric intake vs. out put.
The apps will tell you based on your hiedght, what your BMI is and how many calories you need to consume to stay at the weight your at or lose....in your case, you will take the calories for the weight you are at and increase caloric intake by 300-500 per day.....Extra Peanut Butter and Jelly Sandwich and glass of milk, a Milk Shake, Ice Cream, or Meal Replacement drink....
Eating large quantities of extra food may be hard for you which is why I recommend the high calorie liquids before bed.
When you sleep right after eating, you metabolism slows down helping you to store the food vs. burn it.
Whatever you do, try to add Healthy Calories....Not Fast Food or chemical laden sweets....it will come off easier if you get more fats and calories from a cup of nuts each day, avacado, coconut oil etc. These fats without added sugars will help you gain without causing insulin spikes in your blood sugar....better for baby and you!
Ice cream at bedtime. You'll get calories and calcium. That's what my doctor recommended