The first mistake was buying a weight gainer, especially from GNC. Good weight gainers can be made yourself with quality products and without all the sugar (whey, steel cut oats etc). BTW I really doubt 20lbs in 3 months of pure muscle will be possible for you. Read up at some of the major lifting sites for a while before you start.
BTW Nik, lifting 2-3 hours, even if its only three times a week is going to lead to over training. And what Josh wants to do is bulk, which is fine, I just hope he understands that while you do signifigantly up your calorie intake, those 5-6 meals are not big ones, they are just spread out throughout the day, and should only sonsist of healthy foods (lots of good carbs, lean meats, lots of protein, milk etc).
Josh before you invest in just a weight gainer you want to get the basics, fish oil, whey, a good multivitamin (NOW adam or Animal Pak are good). Creatine will also help your goals, but make sure you do your research before you go ahead and buy stuff, know exactly what you are putting into your body and how it works.