Prenatal yoga?

I've been trying to get back in shape before baby gets here and I'm at a bit of a loss as to where to start. I'm almost 20 weeks. I've started swimming laps again, (swam competitively in high school) but I'm careful to not push it too hard. I'm trying to walk a bit too. Is it okay to start running again? I used to run but it's been a few years. Also, does anyone have any recommendations on good prenatal yoga poses/routines to do or videos to watch for that? I'm not looking to spend any money so suggestions of free resources would be great