Hello!
Knowing me, I’m probably making some gigantic misunderstanding (and probably posting in the wrong section [sorry]),
but I am a user of Ableton live, and whenever I try to export a track, making sure that nothing is clipping of course, but is at max. gain taking this factor into account, all of my tracks in iTunes and on Soundcloud sound noticeably quiet next to Deadmau5’ roaring majesty…
Hope you can help! Thanks! 
That’s perfectly normal, and if anything means so far you are doing everything right!
Mastering is the process that normally brings is up to volume. There is an ongoing debate about the merits of making things louder in the producer scene in general aka the “loudness wars”.
There are many things you can do to increase the volume of your track with compression, limiting and various other things, but these normally come at the expense of dynamics (thump to you and me).
That’s cool, thank you for your help, and I’m certainly not into all the loudness wars at all. It’s just the fact that my songs are almost inaudible next to other things, and the concept that I don’t understand in my limited knowledge is how, if a song is already clipping on the master track, even at the mastering stage, how could you increase the volume without it going all… well, clippy. 
By keeping the louder parts as they are, and increasing the volume of everything else.
This increases the perceived volume and makes the track as a whole sound louder, but will be ‘flat’ with no punch and impact on the drums etc, like just playing a noise.
Have you got a limiter on your master? If not, this is the reason. For me the most you can get out of the Ableton limiter is about 3db of compression at the busiest part of the track. After that you are better off looking at what is peaking the limiter. Usually for me it is the transient for the kick and the snare and the bass hitting at the same time, so by side chaining the bass and moving the snare a little before the kick it gives a bit more room to push the limiter.