Does the pedal go all the way to the floor at times? I would check all of your brake caliper pistons and make sure they go in all the way. Check all of your caliper sliders and make sure they slide all the way in and out freely. This is just to make sure you don't have any frozen calipers or sliders. If your fluid is topped of then you might have a leaking master cylinder if all the calipers are good.