Hun i have no idea of your situation but i can tell you that what you have said is totaly normal. i have a partner to step up when i get frustrated enough, ihonestly have no idea how all the single parents stay sane!
You are doing what you can to improve your life and your DD's life, that alone says that you are trying and you love her.Please go easy on yourself, none of us are perfect and i am pretty sure that most of us have felt the way you are feeling at one stage or another.