Welcome AllieJane - As others have said maternity leave is a personal choice. With DS I planned on 3 weeks off (same as you), although I was tired and ended up only working 4 day weeks in the last month (had to take unpaid leave for the 5th day a week, but it saved my sanity). I finished a very stressful week on the Thursday, waters broke on the Saturday night and baby was born on at 330am Sunday morning. So only had 2 days off instead of 3 weeks! But was glad it happened that way around, as I had extra time to spend with DS afterwards.
PC I keep laughing at your "hope baby won't be born on my birthday". We told DS very sternly while in my tummy that the only day he could not be born was our wedding anniversary. I thought it was a big joke, because that was 3 weeks before my due date and thought it would never happen! Guess what?? Quite right, he was born on our anniversary (which we've decided simply to shift to the day after/before his birthday each year). That also turned out to be Easter Sunday when everyone in the maternity ward seemed to be on leave and so staff shortages galore made things a bit of a nightmare for the birth. So for number 2, we've not "ruled out" any dates.
ZoeZebra - "so over being pregnant" - boy do I know what you mean! I loved being pg with DS, but this pg has been a bit of a nightmare. I now have a bad cold & ear infection & "night" sickness (so no sleep at night), plus roadworks in my usually quiet road, and a neighbour who has been busy with the chainsaw (so no sleep during the day). I might as well get it over with and have bubs now, as I'm not getting any rest anyway!