At 16 I was doing fairly well playing varsity football but I knew I needed to increase my weight and strength for my final year of High school ball. I started at 175 lbs at 5'10. I just fooled around with weights before that, nothing of a serious nature or planned out workouts. That summer a program of Squats (20 reps...sometimes 25-30 reps..heavy forced breathing), BB rows & BP's were done three times a week. Always a set of pullovers after the heavy breathing squats. The program lasted 6 weeks and I gained a little over 30 lbs, with my waist about a 1/2" smaller than when I begun. My chest increased a little over 4". I did have an advantage in that I'm a easy gainer, with a large bone frame even than and there were usually two very large gentlmen pushing me through each training session. Always added more weight, even if was only 1 1/4 plate each side of the bar. After the weight gain I took a week off and than began working in a power rack, being concerned with power cleans, rack pulls, DL's, jerk presses, squats, etc. Was working towards strength and quickness/speed for the coming season. I kepted working out once or twice a week during football season and weighted around 215 or so at out last game. My first year of college I was about 230, in good muscular shape.
I drank a gallon of milk every day, adding dry milk powder and raw eggs in a blender. Also added a pint of ice cream from time to time. Trick is to sip those milk drinks through out the day rather than chug-a-lugging them at one time. Even put cottage cheese (taste like buttermilk) or tuna (taste like fish) in water and mixed in a blender on occasion. I can honestly say that at my first day back in school some people I've known most of mt life walked pass me ...did not know it was me because of the size gain.
Football might consider going on a short but intense lifting program with the attention on heavy compound lifting exercises like the breathing squat, rows, cleans, dips, SLDL's, etc. for a muscular weight gain. Probably three time a week or at the least, twice a week. You have the whole half of this year to get ready for some serious stuff next season. As far as supplements go, most young guy's your age do not need them no matter how their hyped in all those make believe muscle magazines. Good whole foods can give you those magic gains your after if you combined them with workouts taken with serious intent. Good Luck.