I do agree within @Winterwoollies with my experience and those who I know.
I was already a healthy weight to start with, I kept active and ate healthy during my pregnancy, non of this eating for 2, after my birth my stomach stayed swollen for about a week then went back down, the skin was a little more slack.
I had to have stitches so was not moving much after, I also breastfeed I was advised that helps flatten your stomach (not sure if it's true, but it happened to me). But I probably ate a much more high calorie diet while breastfeeding but it didn't increase my weight.
I used a good cream as soon as I found out I was pregnant, it was a boots own cream, I think, but I don't have one stretch mark luckily.
I felt normal after about 2/3months body wise.
I have friends who were slightly over weight to start with, there diet wasn't great through pregnancy so put a bit of extra weight on and really struggled to shift it.