Is it normal to feel like a bad mom?

I don't know why but sometimes I feel like I am a bad mom. I have an 8 year old son and a 9 year old step daughter. I work full time, pack their lunches every morning, make them dinner every evening, do their laundry, clean the house, etc. I've never hit my kids or anything like that. I guess I have guilt for my attitude. The kids are very high energy and like most kids do things like make messes and lie about little things. Like I said I work full time and I work with toddlers all day so when I get home I'm exhausted and sometimes grumpy. I feel like I give them attitude too often and then when they go to bed I think about it and feel like a bad mom. I feel like a good mom is cheery and mostly positive around their kids while I am grumpy a lot of the time. Does anyone else feel this way? Is this a normal thought to have?