Signal repeaters make signal worse?

I started a new job and the building I'm in has terrible signal. By the end of the day, i'm down to 50% battery because it spends the whole time looking for signal. (I know it is not just my phone because it goes all weekend without charging). I purchased one of those stick-on passive antennas that mounts to the back window of your car to set up in my office, but it seems to have made the signal worse. I can't afford one of the $$$ permanent mounted repeaters and I can't rightly go mounting that in my office anyway.

Does anyone have any suggestions on how to fix the problem or how to better mount the antenna??

Real answers only please, no trolling.