Need some help

So let me start off by saying how much I love my sweet, ambitious, feisty 2 year old daughter. I pay attention to her by playing, teaching, and nurturing her. I try to be patient and understand that toddlers are notorious for not listening and pushing boundaries. However, her father and I have fallen into this parenting pattern of yelling at her the minute she does something wrong. We yell and if she doesn’t stop we spank her. I’m literally crying as I write this because I never wanted to be “this” mom (who has no patience and yells & spanks). I know this will affect the way she deals with people and life and I’m so ashamed. Every night I go to bed hoping I’ll be better with her tomorrow. I just can’t seem to learn how to gain the patience and strategies to not snap. It’s gotten to the point where she jumps in fear if/when I raise my voice. I’m so disgusted with myself and feel like a terrible person. It’s no excuse, but I am nearly 5 months pregnant (hormonal as hell) with her little brother and I PRAY that I can be better by the time he’s born.

I guess I’m asking for advice from mothers who’ve been through the same/felt the same way while raising their toddler(s).

I’m also asking for strategies and/or tools for dealing with this and how I can reverse the affects it’s already installed in my daughter.