Why is it hard to shoot 3 pointers?

I've been playing basketball for a while but every time I shoot 3 pointers I only get 2 out of 5 in. The ball feels so heavy when I shoot from the 3 point line. I have to almost basically throw the ball. I don't have this problem when I'm closer to the rim but when I get further away such as the 3-point line I have trouble shooting the basketball. Its not my accuracy that is the problem its my strength. I'm pretty skinny but I can still shoot the ball and I'm actually pretty tall compared to others. Is this because I'm just weak or don't know how to handle a basketball properly? I've noticed that there are skinny people in the nba but they can shoot 3-pointers just fine, so I don't know what's the problem. The ball seems heavy and that I have to use more force. Is it that I'm weak or just need to practice on shooting more often? Any idea?