If you're five foot nine inches tall, I doubt you'll qualify for HGH supplementation unless you have a diagnosed hormone deficiency. Besides, you're 18 and probably have another growth spurt left in you. HGH supplementation at this age might permanently inhibit your natural production. Also, be careful with PH supplementation since hormonal imbalances might cause your bone's growth plates to seal off and stop any future growth not to mention many other potential problems since you're still in the midst of puberty.
Besides, I have short friends who would kill to be 5 foot 9.