93 camry brake light problem

My light on the dashboard for my break keeps coming on. It comes on approximately every week. I top off the break fluid and it goes away but a week later its back on and i have to put more fluid in. I had my rear breaks done about 2 months back and it was right after that that this problem started. Does anyone have any ideas of why im going through the break fluid so quickly? There is no leak ive checked that so it must be going somewhere. Any help would be appreciated.

There is a leak, albeit hard to locate. The only way the fluid can disappear is by leaking out. Possibly it is leaking into the vacuum brake booster and then sucked into the engine and burned.