Leaking...

I am 20 weeks pregnant tomorrow. Yesterday and today I have been leaking a clear/whitish substance. Doesn't really have an odor but I'm worried for some reason. At my last scan a few weeks ago they told me I had low lying placenta but was  hopeful it would move as I grow. Anyone know what this is and/or if I need to go in to ER? I have my next appointment/exam on wed with my OB. Thanks!