I'm on the skinnier side too, but trust me you do need to eat more. Even if it fucking hurts to eat more you just gotta do it. Even if you think you're about to throw up you gotta do it.
I was always really skinny, weighed about 65 kg a year and so ago. Now I weigh 83 kg and I'm still pretty lean. It's because ectomorphs (the body type we probably are) find it really hard to put on any sort of weight, fat or muscle, and the only way to do it is if we eat a heap of food. Good thing about us, we don't have to worry about getting fat and losing weight to lower our bf% is easy as hell. Bad thing though is that we have to eat more than others to make our gains.
oh fuck me.....