Your too young to screw up your system and shut down your natural systems. Ideally now would be the time to go to a lab and get a testosterone base line. This way in the future if you experience a significant drop in test it should be easier to get on TRT (Testosterone replacement Therapy).
Get your diet right with a slight positive intake and you will start gaining size. The hard part for a lot of young guys is the cost of healthy foods compared to non-healthy foods.
Unless you have a plan to compete in something that PED's are accepted or cycled on and off to pass tests, stay natty as long as you can.