I have a problem i have trouble putting on mass. I am 17 5'7 150pds. i started workout last school year at 5'4 weighing 115pds. i gained 35 pds of weight, i have a nice upper body, big chest for my size. My arms and calves are the hardest to grow. I gained a inch and half this year since oct-may. i belive i am more of a ectomorph, but compared to the other slim kids i look but better, like buff. I guess its because i am young. I Want to stay natural for awhile, i've taken creatine, whey proetein , and weight gainer. What would you recommend to help me gain mass, and size on my arm naturally. And have any one of you all had this problem before, PLEASE RESPOND AS SOON AS POSSIBLE