Yep, milky watery discharge is very very normal and called leukorrhea. It's caused due to the increased blood flow to the vagina at this stage, as well as the estrogen levels.
I've had it since 17 weeks and it's been driving me mad, because I was always worried I was leaking fluid. Went to check it out several times, every time it was just discharge. However, always do go to check it out, even if it is to put your mind at ease.
From what I've been told, amniotic fluid is like water, and you're more likely to confuse it with urine rather than discharge. Amniotic fluid will not cling to your labia, so if it's spread throughout your vulva, it probably is discharge. It can dry white, yellow or transparent.
I was told that the lying down test actually works. If you lie down for an hour and then you stand up and there is a gush, better check it out. If nothing falls out, it's probably discharge.
Very common and quite annoying really. I now have some 'dryer' days but every time it comes back it drives me mad.