Use wheel as posted bye Gribouillis.
PyMongo has C depencies so to avoid this Installing from source on Windows
Go here,when dowloaded your version.
Do e.g pip install pymongo-3.3.0-cp35-cp35m-win32.whl
Wheel(.whl) has all C depencies packed,no need to compile.
If you are on MS Windows, save yourself the trouble and install the Anaconda python distribution which comes with a native package manager called conda. Things which are extremely difficult to install on windows (e.g. Numpy, Scipy, Intel MKL dependencies) become a breeze without having to deal with weird dependency issues/wheels etc.