I believe you could have put that weight on in a year because you were so far underweight... The weight you were at is near starvation... You still have a way to go though my friend... At your height and age, you have a lot of growing to do... Depending on your goals, changing your diet will help as well as developing a better routine in the gym, mixing it up and shocking your muscles... You have really just begun... You don't want to start considering this until you are years in and have developed a lot more... There are great supplements you can take now to start with growth... Look into GEAR, N2bulk, creatine powerchews... These are all going to be very helpful for you...