@OP:
Ok, couple of things; First off, if you are...shall we say, "finishing" at about 1 o'clock in the afternoon and you're drained for the rest of the day, that sounds to me like fatigue (and perhaps mild depression) more than porn addiction.
Secondly, you did not tell us whether you are single, married, whathaveyou. I will assume you are single. Had you said to us, "my wife/girlfriend loves me, and her sex drive is strong, but I would rather go watch internet porn" then I would say you have a problem.
It sounds to me like you're basically taking a "break at work" (so to speak) and not coming back to work. Since you are your own boss, you can do this without repercussion. The being tired part actually would concern me more than a daily porn trip from the keyboard; I mean yeah you may need a few mins to cool off after a session, but the rest of the day??
Start checking things like your diet/excercise program, and how active you are outside of work, before you start calling any shrinks. :2 cents: