Girls, how to differentiate vaginal discharge from spotting?

Girls, how to differentiate vaginal discharge from spotting? Yesterday early in the morning I had a trickle about the size of a teaspoon, when it dried there was a light spot, and overall the discharge is light, when I walk for a long time they come out. Can I go to the polyclinic for an ultrasound to check the amount of water? Or should I go straight to the maternity ward? What will they do - a test or CTG, or ultrasound? How does the procedure work when you visit?