You're a little on the light side for AAS, but for 5'6" you aren't skinny as f***.
Ultimately, speed is dependent on strength:weight ratio. So, with that in mind you are going to want to get as strong as possible with as little weight gain as possible (if sprinting speed is the primary goal).
Epistane is probably you're best bet for grey area AAS, but you'd have to watch out for joint pain.
Proper programming with strength and power as your primary goals is what will help you get faster (along with practicing the application of that strength by, you guessed it, sprinting)