Well, it must be stated: Too much is too much!
If you are facing continuously more and more work, more and more tasks to be done then the simple crude but unattractive answer is: You are doing too much!
And here we are at the very difficult situation that you have to decide what to drop.
Before deciding keep in mind that a lot of general commitments for jobs, tasks or projects come along with a lot of tiny (administration) tasks that one usually doesn't get aware so easily. Samples:
- Just one or more short phone calls.
- Archiving of paper (or files) that gets produced along with the tasks.
- Reading of mails, documentation (or blog posts ;-) ).