I have been pretty down about this lately as well. You are SO not alone. As evidenced by all the other amazing mommies in this thread telling you so
I think that no matter what we do, how great(or not so great) of a day we have with our kiddo, we're always going to feel some level of guilt. I guess we just have to accept that, but realize that as long as our child is happy and we're doing the best we can, that that is all we can do.
WAAAAAY easier said than done, I know. (((hugs)))