Hi Janos,
I have felt like this too!
I'm absolutely sure your neither a bad employee or a bad mother! There would be something wrong if your life hadn't been turned round about when you had ds, how can it possibly stay the same?!
I have a friend who had a dd the same time as I had ds 6 months ago, she seemed to take to motherhood like a duck to water whereas its been a bit of trial and error for me, but I'm absolutely sure she has her moments too. What you see on the surface is not necessarily how things really are. I bet others think you are managing just fine too! Of course its a struggle sometimes and every day can feel like groundhog day!
I feel just the same as you often and am sure others do to. I just skim the surface of the housework, can't remember last time I hoovered upstairs, (and feel guilty as I should be playing with ds instead), barely see my friends and god only knows how I am going to manage being back at work (tomorrow!!) 3 days a week on top of everything else. it only take a bad night with ds and I'm in tears the whole of the next day, the tiredness can really get you down.
How old is your ds? Do you have a partner / family who can help more so you can have some time for yourself? Is it possible to reduce your hours at work even just a little bit? Are you depressed, could your GP help?
I know there is enormous pressure to feel like you are performing perfectly at work, and every other area of life, once you have a baby, but I've decided that if I even turn up that's a bonus at the moment, my priority is my ds, and I used to be a career woman!
Your ds will not even notice how frazzled you are or how messy the house is as long as he is cared for.
I think you need to take some pressure off yourself somehow, maybe by working out what you can let go as unimportant, like some of the housework, and just focus on the really important things i.e. the health and wellbeing of you and ds and make sure you get a break.
I think as time goes by things feel less of a struggle, or maybe its just we get used to it, try talking to other mums who I'm sure feel just the same as you.
Hope you get some good advice and support from other mums, sorry this is so rambly