Why can't I do an ollie?

I just started skateboarding 2 months ago. I have only practiced moving around and picking up speed, so now I'm very good at cruising on my skateboard and turning and stopping and the rest of that stuff. I can go pretty fast. But after watching Mike V and Chad Muska, I think it's time to learn some tricks, so I thought I'd start with the ollie. I watched tons and tons of "How to Ollie" videos with pro skaters, and I know every single step of doing an ollie. I can do everything fine, except the part when I have to bring the side of my foot up to the nose of the board (and landing). When I try to bring my foot up, it either goes off of the board or I just jump off the board and land on my without the skateboard leaving the ground. What's wrong with what I'm doing? I practice the ollie almost every single day but it's so hard!