why do mom's feel guilty

I've been a mom for over 21 years now and still find myself feeling guilty.
Do you think nothing else matters but your child(ren)? Today, I got my
step-son off to school. After I finished walking the dogs; I came back in the house and fed the dogs.
my to do list seems to be never ending, and all I want is a time to be alone and quite doing nothing. Yet, I feel so guilty as I should be doing something from my much needed never ending to do list(running all around in my head, getting jumbled together). Everybody else seems to have it all together and I seem to be doing this mom thing differently than anyone else. how do you all do it all? I teach part-time outside of the home, then I'm wife,maid,cook,mom,nurse,vet,the list could go on and on....
i know God doesn't give me more than I can handle, so I guess I need to figure out how to do it better... I began typing this and just realized God commanded us to have a day of rest, and no it's not going to church on Sunday, its having a full day of rest in the Lord. I read some Bible daily, but not like I once did. I spend time with Jesus but not like I once did; I spend time with my children but again not like I once did.... why? I ask myself and the answer is I feel guilty and feel as though I'm not good enough.... This causes my relationships to suffer; now that I figured out whats causing it, how do I fix it... How do I stop feeling guilty for not wanting to do anything at times.