Why is my LM3914 circuit not measuring my voltage?

Many possibilities. Your first step should be to test that the LM3914 circuit is working by connecting a known good battery to its input.

You repeated the same link twice so I can't see what op-amp circuit you are using. An op-amp wired as a non-inverting buffer (aka. voltage follower) should work but what op-amp you are using and what power supply you are running the op-amp from are important pieces of information you are not giving us.

Since you have a multimeter, what is the output voltage of the op-amp?

Edit:

OK, it starts to make sense:

* The 741 is not a single-supply op-amp. It won't work correctly in that circuit because its output can't swing down to ground. You would need to connect its negative supply pin (pin 4) to a negative voltage.

* Resistors Rg and Rf are probably pulling down the voltage on your LED.

You can fix both these problems by using a single-supply op-amp such as a LM358 in the voltage follower configuration shown in fig. 27. Note that the LM358 has 2 op-amps in one package. You only need to use one.

http://www.ti.com/lit/ds/symlink/lm158-n.pdf