I'm petite and can eat whatever i want but find it hard to put on weight. how could i go about that?

If healthy, protein: If you are feeling well, and ideally have been evaluated by a physician recently to be sure you do not have a metabolic condition (such as thyroid disease or diabetes) and are not taking stimulant medications, then adding a protein supplement to your regular diet--without reducing your usual intake--can help. This can be as a snack bar, meal-replacement bar, or powder you add to drinks.

Lift weights and....: First, make sure you get high quality, high calorie foods. Add olive oil to pasta before you add the sauce. Put oil on your bread, and in everything you can. Snack on nuts. Make granola. Eat hummus. Try to increase your calories by 500/day. Then start lifting weights so you add muscle instead of fat. You'll look and feel great!