Protein, eat healthy, sleep, train hard. Creatine would be OK, and vitamins.
At 20 you are still producing more than enough test on your own. It just takes hard work - change up your routine. If you normally do 10 reps x 3 sets, try 20 reps x 5 sets, or 5 reps x 10 sets, etc. something ridiculously different for awhile.
Grab that next higher weight on the rack and do 10 "Even though you can't do 10". Grab the smaller weight on the rack and do 100 reps, go crazy. Supersets, opposing muscle groups, all kinds of crap. Just keep your body guessing. Do Squats, they wake your whole body up.
Don't mess with prohormones or juice at your age - you want your d1ck to work in college, or if not college, at McDonalds, right?