My mom is stealing my money help!!!!?

Ok, here is the situation. I have just turned 18 and my father and mother are currently separated. My father pays alimony to my mother every week. My mother spends this money on new purses and shoes. Is there any way i can access this money. Also, i live with my mother currently but am willing to move out if i can receive small temporary payments from her and my father. What would be the best way to handle this from legal standpoint?