T. you can add calories and keep it healthy by adding more protein such as fish, beef, chicken , pork and soybeans. A great way to add these is by using canned tuna, salmon, chicken and turkey in salads, sandwiches and even stir some in to some mac and cheese. Add some mayo to these canned meats and have it on hand in the fridge with some whole grain crackers for a quick snack, I think you can probably talk your other kids into sharing these snacks with you and it will not even take a minute to pull out a box of crackers and a bowl of tuna, salmon, chicken or turkey salad from the fridge. Throw some sliced cheese on top or even better sprouts or lettuce and it's complete.
Another way to add calories is whole milk and whole milk products like yogurt or cottage cheese. A whole milk yogurt or cottage cheese with fruit and a sprinkle of toasted wheat germ will give you and your baby the much needed calcium to keep your bones and teeth strong and extra fat will help develop your baby's brain. Also defenitly add 1 if not 2 glasses of whole milk in to your daily routine either with breakfast and dinner or a quick glass in the afternoon.
Try to avoid packing on pounds with ice cream and chips and fast food and other snack foods that will only contribute sugar and bad fats. These will not benefit you or the baby, you want to add weight through good nutrition and not high cholesterol. Someone else suggested ensure drinks and those are a great way to boost nutrtion but they are NOT meal replacement. Also protien bars are good to have around for convience try to look at the ones with the least amount of sugar, sugar doesn't nuture and part of your baby's development.
Please feel free to ask me any questions as I would be happy to help you. M.