Keep losing patience

I have a 3 month old and a 21 month old who is cutting her two year molars. She def isn’t feeling the greatest but lately kept hitting.. hard. I lost my patience and she hit me so hard I screamed at the top of my lungs. I felt so guilty I then burst out crying. I don’t know how to get her to stop hitting me and my husband. And I can’t seem to control my anger now. I just lash out and yelled at her. I can’t tell you guys how guilty I feel. Worst mom award ever. Ugh. Two under two has been an adjustment and I’m obviously working on it. But damn… I’m upset with myself.