I also apologize when I have to call repeatedly, or for "dumb stuff". Example: we have certain lab results that our policy requires we call within 1/2 hour (critical results). Even though the result doesn't need to be treated immediately (like a low calcium level in a pt who also has low albumin levels) or isn't all that much higher for that pt, we still have to call. Plus, the lab will not call all the results at the same time. So you call for the first critical lab, then 30 minutes later they call another one on the same pt, so you have to call again.
Sometimes, you have to call again right after you talked to them about something else, such as new symptoms, or the pt just told you they want something else (that they failed to mention to you earlier or to the doc when he was just there, but now all of a sudden it's urgent). Or the pt deteriorates.
I just say, "Sorry to have to call you so early (7am), but I have to call you XYZ lab," or, "Sorry to have to call you again, I know we just spoke, but since I last talked you, XYZ has happened."
Again, I feel it is just a courtesy to recognize that the MD is as busy (or tired) as we all are.