A li'l pee problem
It happens to the best of us, chica. It's entirely possible that you could have a weak bladder, in which case that would be something to take up with your doc. Yet, it's easily as likely that it's simply a matter of cleanliness.
You may be being a little too speedy during your time in the bathroom. If you don't take your time, then chances are that you're not finished your business by the time you get up and out. Your body doesn't recognize the sudden change and it still lets some slip out. It could also be that you're not properly wiping afterward.