I'm not 100%, and neither is Dr. Google. There are lots of stories that go both ways. My MW did say that it's normal for discharge to become more watery (I asked because mine is watery). Apparently there's a strip test that your health care provider can do to tell you if it's amniotic fluid or not. I think I remember reading about a way to do it at home too, let me see if I can find it again.
More watery, yes. More of it, yes. For my first I started wearing pads because the discharge was grossing me out, but I've never had it in that quantity since then.
And I uh.... definitely peed myself yesterday.... I sorta needed to go, and then I turned on the tap at the same time baby did some weird wiggly jiggly thing and yep... had to change my pants. I was only sure it was pee because when I kegeled hard and crossed my legs, it stopped. Hah. Sorry, way TMI.
as far as distinguishing between amniotic fluid and the other stuff...I heard amniotic fluid has a more sweet(???) smell. Your mw or dr can definitely do a simple strip (ph) to check if it's amniotic fluid - you should NOT need an u/s. Dr google could probably tell you the approx ph of amniotic fluid and the strips might be easy to find at the drug store or health food place...if you want to avoid the office and DIY.