Being a good mom

Does anyone else sometimes feel like they are not a good enough mom? I only say this because I yelled at my son (who is only 7 months old!) because he was having difficulty going to sleep. I knew he had, had a hectic past two days, but I still yelled. I look back and regret it very quickly because he is only a baby and is just tired. When there are those moments, I feel like I am just not a good mom. Yeah he is happy, but aren't most babies? Is this just me or am I just being dramatic?