Take a weight gainer protein shake for post workout recovery and some dhea to stimulate extra testosterone production all the while working out 5 days a week. Also, some form of nitric oxide will help give the pump effect. You'll put on muscle and the continual production of it will be fueled by the heightened protein intake. And yeah, you'll need a diet to go along with that that this is high protein and high carb for a couple years and then see where you're at. You just have to make a plan and always follow through on it, you'll become addicted to the gym and how it makes you feel about yourself before you know it. I cut myself down from about 245 lbs to 210 over the last years via constant cardio and a more moderate approach to lifting. You need the opposite according what your goals are.
I would be very cautious with dhea, especially for a 21 year old with a naturally high test level. The dhea can easily aromatize into estrogen and can lead to severe depressive episodes if estrogen rises to fast, both my father and I react very badly to dhea. I have my wife taking it to try to correct hormone imbalances from birth control an it works well for her mood and recovery.
For test boosters, tribulus works well for stimulation of leydig cells for total test production, and maca works well for binding to shbg, increasing free test levels, though this is more useful in older, 30+ men. The op doesn't need any test boosters unless he has a testosterone dysfunction of some kind.
We tried many combinations and protocols on my father. Pre treatment his test was 320 ng/dl [270-1070]. Herbal supplements got his into the mid 400's but we had to cycle frequently and t was expensive. We finally settled on 100mg test-cypionate a week, which is keeping his levels in the 700's. I suspect, based on his recovery rate and growth rate, his levels are higher than mine now.
The OP doesn't need anything but whey protein, not weight gainers full of sugar, and food.
I re-read the original post, and you are already taking in a fair amount of whey. It could entirely be possibly you need to kick the calories up to the 4-5000 a day range to grow. I'll easily eat 4000+ calories a day when im training heavy and not dieting. This is a lot of food, I would suspect you are eating under 2000 a day and do not know how to properly judge your intake.
A chicken breast is only about 200-250 calories. Can you eat 10 a day? Body building is expensive, whole milk and fats can help.