Hi Lizzy,
One of the main reason for not gaining weight through eating lots of carbs is faster metabolism. Gaining weight for the girls who have faster metabolism should consume more calories than what they burn. So first thing we need to note is that whether our daily activities is of less strenuous, moderate or very active lifestyle. Based on that you need to take more and more calories as more your activity ,more calories we burn.
Also ,we need to also take in to consideration following points in our daily lifestyle.:
1. Try avoiding undue activities so as to reserve the energy.
2. Never skip your meals however you dont feel hungry. Include some of food items like Muffins, Pazzta, bread, dairy products ,etc which are rich in calories.
3. Also, include dry fruits in your diet as they are rich in calories. Include them as a snack and carry in purse with you.
4. Also, try avoiding nicotine and caffeine as much as possible . These substances would lead to further increase in metabolism and burn calories .This is the reason that most smokers have lean body.
5. Drink fresh fruits or fruit juices without sugar .
6. Always carry a healthy snack in your purse so as to eat whenever gets time.
7. Maintian a diary to keep a track on your food and daily activities so as you can note your progression.