Hmm... I wonder if there's any other way to do it... but I do kind of get what you mean... Perhaps your next portrait, you could say to your teacher... "I've done 30+ portraits of myself, most of which are at a 3/4 view... could I do it at a different angle? I feel like I'm not improving by doing the same thing over again..." And if he or she is like, "No, too bad," ask him or her if they can give you any pointers on how to improve. I'm sorry I don't have better advice. You've probably already thought of this.

I guess the only other solution is to draw other people more...

I like insanity.