Originally Posted by recall
You partially answered your question by saying you had your interface too loud. Try and maintain a "baseline" level on your volume pot, and stick to that level most of the time..
you certainly want to check your mixes loud and soft, but having a reference volume will probably add to consistency to your mixes in other ways beyond just volume.
nevertheless, if you like
your mixes don't toss them, just level them out in the mastering stage. Mixes always come out louder and softer to some extent and even if your speaker volume is locked down, your human ears vary from day to day, hour to hour.
there are plenty of articles and threads about self-mastering, but if you have some budget, sending your stuff out to a real mastering engineer will totally amaze you the first time you do it.