ur car is unsafe to drive not only for you but the other drivers around you.
i work on brakes all the time. If your reservoir is empty, that means brake fluid is coming out somewhere. places to check are 4 bleeder screws on brake calipers, pistons, metal lines. back of the master cylinder which will drip to the brake booster.
I hope you find the leak and get it fixed.

Ps. if the leak is at the master cylinder, let a pro take care of that part specially if you are not mechanically inclined.