I had my son thirty years ago when we didn't even have blood sugar meters. I went swimming every day (twenty lengths or so, if I remember), ate properly, walked a lot, breastfed afterwards. Don't worry too much and do your best. But if you can do something gentle every day in the way of exercise it really does help.
Swimming is great because it takes the weight off your feet too. Though I could only do a very "old lady" breast stroke. I'm a really **** swimmer! However, I was back in my jeans ten days after the birth so that was a bit of a bonus!