It would be silly and dangerous to give you an answer without knowing more of your stats. Have you run AAS before? If so, what and for how long? How long have you been training? What's your BF%? And above all, your age.
agreed, at 18 you may be too young for this. If you are going to use clen start with a very low dose and do not go beyond 80 or 100 mcgs. You could also look into albuterol, less harsh than clen, but may also be less effective.