Leaking?

I have had 'normal' discharge so far this pregnancy - I'm now 18 weeks. Last week I had what I felt like was water leaking out - left a spot on my underwear. Every so often since, I get random spots similar to that - small, dime sized spots in my underwear - but it's watery and doesn't smell like urine. My dr wasn't concerned last week. I've had an ultrasound since (not at dr..at a place to find out gender, but they are required to report to dr if they see concerns) But I'm starting to get concerned. I go to dr on Thursday. Thoughts?