Size matters

Question
I'm 6'0" 170lbs I am going to school to play Div II ball next year. I am trying to play running back or safety. I have a hard time gaining weight despite eating constantly and hitting the gym HARD several times a week. I keep getting stronger but the mass just wont come i have tried many different supplements and diets but my body just seems to be on its own schedule. How can i put on this weight in muscle? i am trying to be around 185-190. if i put on that weight what drills can i do to keep my speed and agility up because i currently run a 4.37 and i would like to keep it under 4.4.

Answer
  John just keep doing what you are doing.  Size is great, but if you a little smaller and are really fast, just play at that weight.  You are still young and your size will come around age 19 to 20.  Keep working hard and stay on your routine.  Be sure to keep up with lots of eating, especially proteins.  GOOD LUCK COACH NOEL!