It is interesting that anyone would have a hard time gaining weight during pregnancy, because it is more or less an obvious thing. Given the cravings and the appetites that pregnant women have, it will be an obvious thing that you will gain some weight during pregnancy. Those women who were underweight need to support their pregnancies and therefore will have to gain some weight somehow. What this means is that you need to eat healthy, since you want to gain healthy weight. In other words you need to start eating healthy whole meal cereals like brown rice and brown bread. Depending on the amount of activity you indulge in, your weight before pregnancy, your general health and your genes, you will need to eat a certain amount of food everyday to be in the right place. To get the right calculations you will need to see a nutritionist who will make these calculations for you. Take a lot of water and exercise too as this will rid your body of the toxins accumulated in them. You will gain healthy weight when you do not have any excess in any patt of your body and you are not always weak and tired.