Ugh same here.... My second daughter is 3 right now and boy can we have bad days. Some days I really don't know how to deal with the behaviors and it can be so overwhelming, Then I get that guilt feeling that I did not do the right thing which makes me feel a thousand times worst. I don't have much advice but I get what your are saying. What I have started doing when we are in any rough patch, arguments or whatever and I don't know what to do ...I stop and hug her. It kind of helps defuse the situation and calms me and we get back to 0. It does not work all the time but most of the time it does. We can talk it out after she is more receptive and I make more sense in my discipline choices.
Stay strong and like the other have said ... Tomorrow is another day.