I am not a bad mom but why do I feel like a bad mommy?

Lately I have had time to think about what I do and how well or how bad  I do it. I have been a stay at home mommy and my husband works 4 ten hour days so I am here till 530 all by myself and at times I want to run and hide.
Is that wrong? I mean as much as I love my son I want to hide sometimes and just come out in a couple of years. Is this normal? I would think that maybe yes and maybe no. I was so used to working for so many years and have the freedom to get up and go where ever I wanted when I wanted. Now things have changed drastically, I mean I cant just pick up and go when I please and if I need to rush off somewhere I still have to plan for the rush.
I find myself though at times wishing I had more time in the day for me and that I can spend more time just relaxing. I pray that nap time will be more like 3 hours instead of 1 and I know its wrong but I get excited at bed time.
Sure I am not gonna win mother of the year nor worst mother of the year. But I know that I am not alone. I know that there are other stay at home moms and dads out there that feel like I do and pray that God will make nap time last longer. But why should I be ashamed of being a stay at home mom who needs to sleep an extra day just to feel like her self?
So in order to compromise being a stay at home mom and wanting something for myself I have decided to go back to school. Now this may seem wrong to many but I think that I am on the right path to making ME the priority. What am I gonna study? Well believe it or not I am going to go get my credential to be a teacher. I am gonna first go and study child development so that I can work in a day care/preschool but its something that I have been wanting to do for awhile and just put it off because i felt it was not ok to leave my son.
So inspite of thinking I am a bad mom I think that my son will proud that his mommy did something for herself and this will help me be a better mom and wife. I think that in the long run I will be glad I did this because I know that I can do all things through Christ who strengthens me and I have faith that God is the one who will guide me and give me the extra time in the day to get things done.