I have issues pumping my tires too. Here's what you have to do... you have to unscrew the presta-valve all the way... and then tap on the top. For some reason, they can get... stuck... and then when you try to put air in, the air won't go in. Sometimes it takes a few tries of me putting the pump on... taking it off... tapping the presta-valve... trying again.

I have drained my tires of all their air sometimes because that stupid valve gets stuck.

Sometimes I worry I won't get any air in the tire because it gets stuck.

Because of the above reasons I HATE PUTTING AIR in my TIRES!

Try tapping the presta-valve and pumping it then. If you are pumping and it feels like the air is not going in, then the valve is stuck.