I'm a hardgainer like you man. I went from 120 lbs to 144 lbs in like 6 weeks using a workout I designed at the website below:
http://sites.google.com/howtogainweightforskinnyguys
Check out the 'Before You Get Started' page, I have a few tips to help make sure you gain lean muscle fast.
If you follow the guide and the workout, I guarantee you'll be jacked by june, no questions