Sex burns alot of calories.
Lean protien (skinless chicken breast, fish, turkey), whole veges (broccoli, carrots, spinach, onion, beets), whole fruit (berries, bananas, tomatoes, apples, citrus), lean yogurt and milk, whole grain cereals, lotsa beans and nuts.
As per exercize, repetition is key, get your body used to working out and you'll burn more calories and speed up your metabolism.