Long QMake and Build speeds

For some reason, it's suddenly taking much longer than it used to for QT Creator to run QMake or build my project. After it's finished it slows down my computer to the point that new windows take an entire minute to open. When I start a build, the fan turns on and the CPU starts running at full power, and it never stops. The fan keeps running and the processor keeps processor at its full 3.1 GHz even after I close QT Creator. When I then try to shut down the computer, I get a screen telling me Windows is waiting for a program to finish its task. That program is explorer.exe, and the task its finishing is playing the log off sound.

All this only happens after I try to build my project. What is going on all of a sudden?