It's also normal because liquids are naturally present that are secreted by the vaginal walls in the course of the day. Their purpose is to naturally cleanse the vagina. It doesn't necessarily mean you were aroused, it's just like your mouth naturally being moist.
Google "cervical mucus" or "vaginal secretions" to see the difference between the normal thin and milky fluid that the vagina puts out (especially in the first half of the cycle) and the eggwhite cervical mucus associated with ovulation. It's often interesting to keep a chart tracking the differences for several months; if you do it on graph paper with each menstrual month on one line, it comes out like a bar chart after a while to show you the normal lengths of your bleeding, when you ovulate, and when you have vaginal secretions of other kinds. That can be useful for projecting forward to see when your next period will probably come, and things like that.
Going on the pill can change the quantity of discharge, but it does not always do so. If it works, the pill will prevent ovulation, so the thicker, clear, stretchy kind of mucus would not be present.
Discharge is normal so long as it doesn't resemble cottage cheese, itch, have an odd color, or smell horrible (fishy is often used to describe a yeast infection). It's just a sign of your arousal at some point during the day or what phase of your cycle you are in. There's no guarantee birth control will lessen or relieve the amount of discharge.