First of all, I don't think that it would be a good idea to start using steroids at this point. At 20 you could cause some real problems for yourself. Let me ask ya a few questions and see if I can come up with any other alternatives to gain muscle mass quickly.
1- how long have you been lifting?
2- you mentioned working chest and arms, what about your back, legs and shoulders?
3- Do you do a pretty standard routine or are you changing things up?
4- Do you do much cardio? I know a lot of people think cardio is just for burning fat, but it pumps blood through the muscles cleaning them out and helping them to repair and grow faster. Also, it increases vascularity helping you achieve better pumps when lifting.

Answer these and I'll see if I can help ya get the gains you want without much effort, and without causing damage to yourself.