Very few 14-year-old boys think they're big enough and strong enough because they can't influence the biggest factor that determines size and strength: simple genetics. Still, there are a number of things that a 14-year-old boy can do to grow bigger and stronger, if not taller. A combination of a well-balanced, nutritious diet and whole-body exercise that includes cardiovascular workouts will add enough muscle and bulk to satisfy almost any 14-year-old boy.
Start with a healthy, balanced diet. Avoid processed foods. Eat plenty of fruits, vegetables, and whole grains. Try to eat more fish and poultry than red meat. Snack on healthy foods, eating carrots instead candy. Drink plenty of water, at least eight 8-ounce glasses every day. Minimize or avoid sports drinks, supplements and anything that even has a brief suggestion of a shortcut.
Exercise properly. Building muscle takes a long time. Be patient; don't overdo it. Do a variety of exercises, alternating weight training with aerobic exercises. Walk instead of taking a car. Take stairs instead of an elevator. Stretch to avoid injury. If you're injured, rest until you're healed. Ask a personal trainer for a good variety of exercises. Keep daily records of your exercise routine and weight to serve as motivation.
Understand your limitations. If your parents are short and fat, it's likely that you'll be short but not a foregone conclusion that you'll be fat. There's little you can do to influence height -- the best you can do is is keep yourself strong and physically fit. Don't judge yourself on your appearance alone. Mental health is a key component of physical health. Being hard on yourself or having unrealistic expectations won't improve your health.