Push-ups/sit-ups diet question?

That is aerobic, catabolic exercise. You wont truly grow any new muscle the way we think of Arnold or Ronnie Colman. That growth is an anaerobic, anabolic pattern. Anecdote time, I saw one of my gyms 45 year old former high school track stars in the supermarket buying chips and frozen pizza, still looking like a desiccated corpse. The carbs go to the energy to perform the running (or 200 pushups). Not to growing muscle tissue. So no, excessive protein is not needed and will likely not be wanted. The body knows what it needs and you'll be craving bread but shoving this milkshake down your throat, still hungry for bread afterwards.

How old are you now? It's quite common for teenagers to be slender, since they're still developing their adult bodies.

Doing only sit-ups and push-ups won't develop your whole body. It might burn a few extra calories, but your running uses more.

If you are hoping for a well-developed physique, find an exercise program that works on all your muscle groups. You may want to join a gym that has qualified instructors.

If possible, eat more actual protein. There's animal protein (meat, eggs, and fish), dairy protein (milk and cheese), and vegetable protein (grains and legumes eaten together, with grains predominating). "Protein powder" usually lacks high-powered animal protein, since meat is best when kept fresh and then cooked.