One thing that has helped me in the past when there has been a discrepancy between "what gets done" and "what should have gotten done" is to go back to something I actually hate to do ....
Keep a time log for at least a week.
It takes a little time from your day but, not only will your boss then know how your time is being spent, but YOU will too. It's amazing how much time I found I was spending trying to get back into focus on a project after having been interrupted. The other big item was that I'm a great "firefighter". I just love to jump up and put out fires - even when it isn't my problem to solve. (just my issues, keep in mind)
At the end of the day, you can review with your boss what you wanted or planned to get done, and what was actually able to be accomplished. The difference is that you will know what it was that kept you from your plan. The other part of that is (if he/she is willing) your boss then has the tools to help you, or coach you in what your job really is. Maybe you're spending time on things he/she doesn't feel are important? Maybe he/she just doesn't have a clue all the things you accomplish in a day?
Be prepared though to see the truth and to be willing to receive some coaching. It can be a humbling and at the same time an extremely enlightening process for both of you.
Hope this helps!