I want to improve my running any exercise to help? am quite fast but have low stamina and my health is perfect says doctors

Runner: Recommend stretching exercises to warm up the muscles. Each session of running push alttle further and longer and you will improve.

Keep going!: Three things come to mind. First, just keep doing your distance runs going farther every 1 week. Second is wind sprints - they definitely help with stamina and it's a faster way to achieve the result than just the distance running. Third is a different aerobic exercise intermixed in your program. I like YouTube "Fitness Blender" workouts. Simple, done at home with or without weights.