A banana has around 100 calories, so does the glass of milk. And both are very healthy during pregnancy
Try adding things like butter, mayonaise, and peanut butter to what you already eat. If you like milk, use whole milk to get some extra calories. Nuts are also a really healthy, high protein snack and have a denser calorie content. Rather than trying to force yourself to eat MORE foods, try and find a few high calorie supplements.