Walking causing miscarriage?

So before finding out I was pregnant I didn't really walk. As soon as I found out I've been trying to walk everyday. I want a natural birth and to go into labor on my own. My other 2 kids I was induced with epidural cause the dr felt I needed it. And walking can help keep you healthy and help with starting labor on your own. And so I'm 5'3" and about 180 so I am overweight. I should be walking 5 miles everyday to maintain a healthy weight during this pregnancy. So my question is: if you weren't really exercising to begin with, can walking 5 miles a day cause I miscarriage? (Mind you I am taking it easy and nice and slow) I'm having a little first trimester cramping/twinging. So I was just curious.