even after I use a multi band compressor and limiter in the mixing process. I take a hard limiter on the final mix, and limit at -6 DB. If the mix never reaches that point, I slowly increase the gain until the song starts to sound like crap. Then I stop and start reducing the gain a little at a time until it starts sounding good. Once I get to maximum gain without ruining the quality of the recording, I stop and press ok.
Once you reduce the severe spikes in volume take the normalizer and normalize to anywhere you like. I like to usually go anywhere from -3db to -1db. It should sound louder and you shouldn't notice any loss of sound quality if you did it right. If you cannot hard limit the spikes you should probably go back to your mix and fix it there because that would be a major problem with the mix, and not just something with a quick fix.
Keep in mind I only finally learned enough about this stuff to even give minimal advice about it last night, so take it for what it worth