You sound like I did. I feel for you, it will get better.
I would agree with plantsitter, you need at least 6 months. I felt like jacking it in almost weekly.
I personally also suffered from 'maternity leave rose tinted glasses'. I couldn't have carried on living as I was (going to lots of baby classes, lots of lattes out, buying DS what I wanted, driving everywhere in our gas guzzler) if I hadn't have gone back to work.
I found maternity leave very magical - you can focus on DC, all that spare time with not much to do! But in my more realistic moments I knew that if I was at home without my salary it would have been a very frugal (and house bound!) life...
It is no wonder it is all suck a shock, prior to birth all you had to do was get yourself up and out, now you have 2 (or maybe 3 if you include DH needing stuff sorting for him!)...plus everything is now on a deadline - get the train to get in early enough, leave on time, get to the nursery on time etc. And I also felt the "shadow" of my former working - workaholic - self leaning over me!
During these 6 months you can always think about what is and what isn't working - there might be things you can change; working patterns, childcare drop off and pick up pattern, working from home etc.
I struggled for most of my first year back with my really full on job. I moved from 3 to 4 days and felt SO much better. I think for me working more made me feel part of the full time working community rather than the SAHM community, I personally felt at 3 days I wasn't either. However I know lots of people who do 3/2 days and it works well for them.
What worked well from us was to write a list of who does what in terms of household (and DS) management, you need to write it all down and then divide it up and keep the list somewhere. My DH is "good" when it comes to being hands on at home, but does need prompting, I have given up hoping he'll think to do x, so we just now have a list!
And yes, keep focusing on the good things about working - more money, continuing a career you worked hard on, dressing up in 'office clothes' (well I do), peace when eating and a chance to go to the shops etc.
I also liked how disinterested staff were in my DS, it was so refreshing! Co-worker: "How is x?", me "Fine thanks". Co-worker: "Great, have you see the Anderson file?" etc.
Maybe set a deadline in June to review?
WS