Time, bro... all it takes is time. You should read the modern encyclopedia of bodybuilding by Arnold Schwarzenegger. It talks a lot about body types in there. As an ectomorph you will always struggle to "get huge" or make big gains. I am also an ectomorph, and it took me years to get used to being one. I always wanted to be the guy to walk around with big muscles, but finally I just realized that wasn't going to be me. The biggest I ever got was 185 lbs. and I'm 6' tall.
When it comes to MMA there are actually a lot of benefits to be had from being an ectomorph. Take a look at guys like Donald Cerrone, Carlos Condit, Nick and Nate Diaz- all ectomorph type guys. Their length allows them to be dangerous fighting off of their back, and their standup is rangy as hell. In the case of Donald Cerrone he is an undefeated kickboxer something like 29-0. Learn to build off of your strengths and work around your weaknesses, I say. Ectomorphs generally have a LOT better cardio than other body types, too.
You're still young, though... you may grow a lot bigger than you realize. Just keep at it, but don't tear up your ligaments trying to lift too much. That's a common problem for ecto's.
Here is a snippet from http://www.bodybuildingpro.com/bodytypeinformation.html
Definitive "Hard Gainer"
Delicate Built Body
Takes Longer to Gain Muscle
The extreme ectomorph physique is a fragile and delicate one. The bones are light, joints are small and muscles are slight. The limbs are relatively long in proportion and the shoulders droop. The ectomorph is a linear physique. Straight up and straight down, and may appear longer than he or she really is, due to the length of limbs coupled with lack of muscle mass developed on those limbs. The ectomorph is not naturally powerful and will have to work hard for every ounce of muscle and every bit of strength he or she can gain.
Other Ectomorph Traits
The extreme ectomorph may have long fingers, toes and neck are long. A pencil neck you could say. The features of the face are sharp, and the shape of the face is triangular. The lower jaw is somewhat receding. The skin tends to burn easily. Extreme ectomorphs may suffer from extremes of temperature. Due to the great body area in relation to muscle mass, the ectomorph may suffer from great heat, and due to low body fat, the ectomorph may suffer from great cold. The hair is fine and grows quickly and is sometimes difficult to keep in place.
Lisa Kudrow, Kate Moss, Brad Pitt, Seth Green, Edward Norton.