Hello, I'm 15 years old, 5'6-5'8, around 105-110 lbs. On average I'm pretty skinny and have been upping the amount of food I eat but I can't gain any weight. I also benches and push-ups and lifting dumbbells but I haven't noticed any improvement. I was wondering if there was a way to build mass and gain weight.

I know what ya mean, but if you ARE planning too box then you dont want to gain. You'll end up doing it naturally through boxing training (naturally as in not forced,) I found that I stuck to one training program it works. I only been training for 3 weeks now and I have gained muscle mass quite well. where do u live?

Obviously, you're not eating enough. Since you're ectomorphic, eat 6-8 LARGE meals. You don't really need to count. Eat until you're stuffed, then 5 minutes later, go back and eat again.

But like speedoverpower said, if it's for boxing, just let yourself gain it naturally.