I'm not a Pro Tools user but do you have any limiter or gain plug-ins that you can use to increase the level?
If not, what about mixing it down, exporting it and then importing the mix down into a new session and increasing the level of the fader again.
Wish I had a copy of Pro Tools so I could help you out better.
Do also look for a limiter style plug-in. That will give you "gain" controls and a "limiting" feature (the level can't go above xxdB). This can help make your audio mix dynamically louder.
At the risk of sounding flippant, next time you record, make sure your levels are hot enough (and avoid clipping, of course!)
If your gain staging is set properly, you shouldn't have the problem of having to crank your mixes.
That has a fantastic mastering limiter for absolutely free. In my opinion it is the best limiter plug-in that there is. Also, use the phase scope plug-in on your master channel and see where your RMS values are (set drop down to RMS) - typical cd mixes range from -14 to -8 while radio mixes can get up to -6. I don't suggest that extreme, I never go past -10. Too much compression will kill your mix. Using the phase scope takes second guessing out of if your mixes/masters will be loud enough when listening on things other than your studio set-up.