I'd wait on the cycle. At 18, you're already on steriods naturally bro - take advantage of it.
If you are interested in steroids, take the time to learn all you can about them. Right now take the time to turn that "pretty good" training into pretty phenomenal training. Record what you do and make sure it's working - if not modify it. You will find that diet is an intergal part of the process.
Pack on the pounds without the drugs for now. Build an AMAZING body FIRST. Then if you are still interested, you will be able to take advantage of the drugs.