I Want to Gain Weight

It'S Been A Struggle... At 6'3, and only 150 pounds, I'm defenitly under sized. This is mainly due to my very high metabolisim, I could eat all I want, but cant seem to gain anything. Throughout this year, I've been trying my hardest to gain some weight, and to put on a little muscle. I'm sick of looking like a twig. But so far little has changed, I've spent a hundreds of dollars already on random snacks and food, and have consumed it all, nothing. I've also been working out 4 days a week as well, but not much for muscle growth. It could be that I'm doing something wrong, or I'm just meant to be skinny. Whatever, could be worse, I could be morbibly obese