how can I stop being mad at my boyfriend all the time

I just had a baby and I just feel really stressed out. I feel like my boyfriend (my daughters father) isn't helping me but I guess he's trying his best. I just take all my anger out on him. I realize it's not healthy for me to be mad all the time. It makes my life and other people around me miserable. How can I not get mad so easily and be nice to my boyfriend even when it's hard for me?