Diana, keep practicing and close your ears to the teasing and laughter. The exercises your teacher gives you are going to sound unusual to anyone who doesn't know what it takes to develop vocal technique. You are learning what it takes, your teacher is guiding you. Trust your teacher and keep going. If you have to go into the shower to practice, do it there or in the car, where the other people won't bother you. Don't give up. Those muscles you are training will get stronger and stronger as you build them up with practice.
IT IS WORTH IT IN THE END. Some day they will realize that you have become a singer because you were willing to persevere through all the training exercises and classes, and when you have that voice polished, no one can take it away from you.

Alice