I have been looking at these forums for a few weeks now and i am struggling to get my mind wrapped around gaining. I am 17 years old and 5'11". I lost 20 pounds over the last year and i believe that i was underweight. I got down to 133 lbs and i had absolutely no energy. I have not been diagnosed with an Eating Disorder but me and my parents both believe that i need to gain. I have been eating around 2500 calories for the past week, but i am extremely active (3 hours a day of soccer practice for high school). I know i need some more calories, but i am kind of worried because i have already gained four pounds (i dont know if it is just water weight or not). I need advice from people who have gone through this.
If your gaining, I would think maybe just stick with that and see if it continues. In a couple days, if its gone back down then you will know if it was just water weight and then you could start adding in more calories and keep working with different numbers until you find what works for you. :)
I know it is really scary to suddenly gain so much, but as you started eating 2500 only a week ago this is most likely to be water weight. Everyone goes through this sudden shock of gaining loads on what they didn't think was that much food, but honestly you will not be the exception to the rule, especially seeing as you are so active - you will need a lot more to gain eventually!
If you know that you need more calories, then eat more calories, because this is the only way your metabolism will sort itself out - it will speed up a lot once it realises that you are not going to starve again. I would say, up to 3000 calories as soon as possible then probably increase again after a few days because of all the exercise you do - I'm a girl, all the exercise I do is walking, and I don't even gain a pound a week on 2700 now because I stuck at it and kept eating...I know it's hard, but believe me you will be ok increasing and have loads more energy once you are giving your body what it needs :)