Well, one reason could be one of you brake lines is leaking fluid or your master cylinder seals are leaking making you to lose fluid. Also, if brake lights remains on all the time, there is a switch underneath the break pedal, it looks like a crayon, check on the floor and if you see pieces of it, it means its what remains of the switch. Without the switch, the brake light will always be on, confusing you into thinking that you are leaking fluid. You can place a small screw and a nut across in place of the switch, it does work. However, I advise you to buy the EOM part as it does not cost much.