I was your height and weight for most of my life and couldn't put weight on to save my life. But I'll tell you this, if you eat like a 150lb person, you're going to be a 150lb person. Ectomorphism is loosely used and a myth unless you have an actual condition. I went from 150-180 in about 2 years time when I started to get serious about it. You can't just eat when you're hungry and only eat til you're comfortably full. You literally have to force feed and be miserable so that your body adjusts to eating like that. Eat a lot and often. That's the only way you'll gain and keep it. Sure, you could cycle and put on a few lazy pounds, but it'll go right away when you come off because you're still eating like a 150 pound man. Most young guys just want to rely on steroids during beach season to get "jacked", and then go back to normal for the winter. They yo yo their bodies every year and that leads to damage. It's lazy and its shameful. When you eat, eat until you are full, then force more down. And eat big before bed as well.