Answer:
All girlfriends are a tease sometimes. For example I'm not very good at tennis or basketball, and when my girlfriend beats me she usually teases me about it and this can make me feel very embarrassed and irritated with her. You just have to put up with this sort of thing and not let it get to you. However, if she's really driving you out of your pants with the teasing, so much so you're finding it impossible to cool down afterwards and you can't concentrate in lessons or sleep at night, then you need to pluck up your courage and stand up to her. Tell her enough's enough and she shouldn't play with your feelings like this, or just ask her sweetly and politely if she'd mind not teasing you so much? If she really cares about you she might start doing it less, and if she doesn't, then ask yourself do you really want a girlfriend who only ever torments you and makes you feel frustrated and cross?