In 2001 I weighed 142 lbs. at 6'2". So, I know where you are coming from. It was hard for me to eat more at first. And, I was afraid of getting fat. Today, according to calipers, I'm at 10.6% bodyfat at 215 lbs. I didn't touch a steroid until I had gained over 40 lbs. I added about 10 lbs. with juice over a 6 month period after that and didn't touch them again until I'd gained another 20 lbs. The biggest thing for me has been EATING (as everyone has mentioned), second has been training (heavy weights lots of rest: ie no cardio unless dieting down for competition), and juice has been only a tool used occasionally to boost toward my goals. Don't get me wrong, I love steroids, they work, but they are best treated as PART of your arsenal- not to be relied upon as some think.
As a side note: When you are ready to use, keep in mind that ecto's like us can grow off of a little juice (read at 500mg. total per week or less for 6-8 weeks) and a lot of food. My last bulking cycle I did just that: 5-6 weeks of 250 mg tren/ 250 mg prop per week. I trained my ass off and ate a lot the whole time and went from 205 (had been dieting) to 233 and ended up keeping 15 lbs. (I'm dieting for a show again is why I'm down to 215...) To those who don't buy that, keep in mind I'd been off for many many months. Anyhow, best of luck.
Jacob