Every time I bounce my tracks, they come out very quiet.
In Logic Pro, you have the option to normalize your track when you bounce. Normalizing is where the volume of the entire track is adjusted so that the loudest point is at full loudness (0dB), and everything else is scaled accordingly. By default, this is enabled only if the volume of the sound you're bouncing goes over 0dB (in order to prevent your bounce from clipping), but you can also set it to "Off" (where it doesn't change your levels no matter what) and "On", where it does what I've described above.
Try setting Normalize to "On".
Conversely, if your levels are going above 0dB, you could try turning Normalize off — but if you need to turn it off to get higher levels then the audio you're trying to bounce is too loud, and you should deal with that before bouncing (perhaps putting a limiter on your master would help, but also checking to see if at any point your master level meter overloads).
One suggestion I have, which is not a complete process of mastering but would usually be a part of it, is to add a limiter to the master track and boost the gain.
This will allow you to increase the average output volume by adding more gain and compressing the peaks. I would try this with a few different settings to see which would best apply to your needs, however, the general rule of thumb is that you don't want the ratio too high or the threshold too low, or you will start to get distortion and lose dynamics.
Again, this is more for you to be able to have a listenable track that is not extremely quiet compared to professionally mastered tracks but it does not cover everything that would be done in the mastering process, so should not be used for a professional release.
While I'm no master at mastering, this guideline might help achieve good results in this mastery.