Why are you recording with low volume? You should be recording as hot as possible to disk. You can adjust the volume after you've done your track. If you absolutely need to sing with your guitar, do a scratch track, then go back and re-record the guitar on it's own, then the vocals on their own. That'll give you more control over the mix. A touch of compression can help but if you can make do without it, you're better off. When you export, use a limiter in the master section to bring the overall volume up if you need to.