Need help in gaining weight!

I know a lot of people who use this probably want to lose weight, but I need to GAIN weight. My metabolism is extremely high and I lose a lot of weight if I do not bulk or hit at least 3K calories a day. Even if I were to go through my day without exercising, I still lose weight. My body fat percentage is about 8%. If possible, can anyone recommend me a diet to do so (a healthy one, not just junk food).