How can I overcome feeling like a slacker?

I am a very productive person, with multiple projects going on simultaneously, both personal and professional. Generally, I handle juggling things pretty well, and accomplish quite a bit. I can usually attain most of my goals, and I like that about myself. (I'm also a pretty ambitious person so I have many big goals.) However, I also often feel like a complete slacker. I can see all of the things I accomplish, but I often feel like I could be doing more--one more thing, one more project. Sometimes, when I look at the things I've accomplished, all I can see are the things I wasn't able to do and it can be easy to feel defeated and negative about that. How can I reconcile the gap here? How can I get better at feeling the sense of accomplishment I think I should--and deserve--to feel? Do you have any ideas for getting rid of this mantle of slackerness I've saddled myself with -- unfairly, I think? I've been making some changes that have helped, such as writing down my accomplishments each day, but I'm looking for more ideas.