I'm 18 (I turn 19 in January), I'm 169.5 cm tall, male, 75.2 kilograms. My doctor today said he wants to up me to 1400 calories for 3 days, then 1600 for the next three, then finally sustain 1800 a day with my current workout regiment (an hour and 15 minutes a day on my exercise bike). He said he wants to see a weight gain and that my other weight gains are likely my body making up for the net caloric loss of 2400 calories per day when I was only eating 1100-1200 calories a day. He said that my body is sort of panicking and converting more glucose into fat instead of my body using the recommended 1800 calories as energy. I'll see what happens over the next few weeks. He wants me to get back up to around 77 kilos and then 6 months from now he said I will have lost (if my workouts stay similar) those 7 kilos and be down to an ideal weight of 70 kilos. I just need to stop weighing myself every day. I'm going to go to once a week to keep track and I'll let you guys know how it goes. Thanks again.