Just add a compressor on your voice-over. Set the ratio to 2:1. Set a middle long release and a bit faster attack. (Or auto if you have it.) Then you lower the threshold until it gets better. Just play with the ratio and threshold until you get it right.
What the compressor does is that if the audio gets over the threshold in volume it will wait the number of milliseconds you set as the attack. Then it will increase 1 dB per 2 dB the audio really increases. This is the ratio. 2:1 is this: If the audio increases 4 dB, the output will be 2 dB increasment.
When the level dips below the threshold it will turn off the compressing (the 2:1) after the selected milliseconds in release. This will turn down your volume, thus allowing you to turn up everything. Therefore everything will be louder, instead of like it is before the compressor: Not loud, with loud peaks. The compressor reduces the peaks, so you can increase the volume to get the overall volume up.
Since the compressor turns everything down you can increase the output gain to turn the volume back up.
The soft knee turns the compressor on gradually, the more knee the more soft in the beginning. It's like this: If you have ratio to 2:1 and threshold of -10.
Without knee (in consept):
With knee (in consept):
The gate threshold is the minimum volume the audio got to have to go through the compressor. A gate is simply a expander (see below) with attack = 0 ms, release = 0 ms and ratio = 999999999:1.
Oh, I see that you have set up the expander! The compressor ratio turns the volume down if it gets over the threshold, the expander ratio turns the volume down if it gets BELOW the threshold. Thus making the sound twice as low if it is below the threshold, as you have set it up now. Set it to 0, because you don't want to reduce what's below the threshold, because you want to reduce what't over the threshold to turn UP what's below it, not DOWN.
The graph tells you how the audio will be affected by the compressor. The x-axis (the horizontal) tells you the input, and the y-axis (the vertical) tells you the output level.