very confused

my ex is taking me back and forth to court. i just dont know what i do so wrong. i do everything possible to do the best things for my children.now all i have is court fees and to fight with my ex. all i want is to be left alone, and take care of my kids to the best of my knowledge. sometimes i feel so alone because i feel lost. i just want to give up fighting. i try so hard to do the best job as a mom could do.i only think of my children, not me. i run around like a taxi monday through sunday. then i have my ex who says that im not a good mother. what am i doing wrong? i dont understand,why i cant cut a break. i work a full time job ,take my kids to school, then dance,guitar lessons and ccd and church. what else can i do.