watery drainage - tmi sorry

So I've had an increase in watery discharge this week. Not a ton of drainage but every so often a blob of watery drainage will make a silver dollar size wet spot in my undies. My OB to be safe is sending me for an US today but said it probably isn't amniotic fluid. It's smells a little musty but maybe urine like must? I don't know what amniotic fluid smells like? I also notice that my dirty undies in the hamper are stiff from where the drainage dried. If it was amniotic fluid would it do that? Currently 17 weeks. Please any advice or personal experiences would be amazing. Very nervous.