Try not to take things personally. Even in professional theater, you come across plenty of actors, designers, directors, and other production types who always see the glass as half-empty, are more self centered than team oriented, and seem unable to read a schedule and show up on time.
While you can’t change other people’s behavior or attitudes (especially when they’re teachers or your fellow students), you can control your outlook and reactions. Keep striving to stay cool when everyone is annoying you. Answering the same question 17 times kind of comes with the job of SMing. I try to remember that it’s just like a show; you’ve seen it a dozen times, but it’s new to the audience (the question is new to each actor).
A couple other ideas:
-You mention sending emails. You may want to get some feedback or ask an objective person about whether your emails are as clear and idiot-proof as they can be. In addition to saying when and where rehearsal will be, you may want have a list with everyone’s name and what their call time is (even if the entire cast is called at the same time). If you make yourself a template for this, and make a habit of sending it the night before every rehearsal, it can be pretty easily done.
-If you haven’t done so already, you may want to make yourself a conflict calendar. Go through all your notes, and put together a calendar that shows you at a glance when Lisa has a dentist appointment, when the stage is unavailable due to building maintenance, when the music director must meet with so-and-so, so you can’t have them in rehearsal then…whatever. Then tell the actors and production team that if their conflict is not on your calendar, it will not be honored.
-For the folks with smaller parts, can they be outside of the rehearsal room, but still nearby, when they are not actively participating in the rehearsal? Yes, you may have to pause to get them into places for their part of the show, but it would mean less boredom for them, and fewer sources of distraction for you and the actors who are working.