Losing my temper

I have a 3 month old and have been losing my temper constantly with my 4 year old since my daughter came along. When my older child doesn’t listen or does something unacceptable (dangerous etc) I lose my cool and yell at him, sometimes grabbing him to get his attention. I might be a hormonal mess still and I know my oldest is still adjusting to having a baby, but I need some advice/solidarity/help. I need to control my emotions better and set a better example for my children but I’m just a mess.