If it's not that your expectations/standards are too high, is something else going on? Are you having a rough time with the kids and finding your groove? (Kids can be bloody hard work).
Could the issue be that you're expectations surrounding being a SAHP aren't realistic? That you happen to hate housework which unfortunately is a pretty big part of being a stay at home parent? (not saying that it should all fall to the SAHP, just that the SAHP at least should make a fair dint in the house duties). In which case I am not sure what the solution would be. Perhaps either pay for a cleaner and/or cease being a SAHP? I just don't know if staying home with the kids and not taking on housework is a realistic goal.