How often is this happening? How old are you?
I'm assuming you're female, and that can happen at times, especially when you're young and everything is new. Just as boys are getting inconvenient erections with random thoughts, girls can get aroused, too.
Discharge is also normal, unless it's clumpy, has an odor, or a color.
Maybe you can carry some panty liners with you that you can use if you need to. You shouldn't need them every day, but they can help when necessary.
hang in there kid. God will help you.