90GB Storage lost after Boot Camp Partition..

Hello,

Went into boot camp with the aim of installing windows, set up the partition to give 90GB of my 500GB hard drive to Windows.

After boot camp finished installing windows and drivers etc, it restarted and was super slow, didn't give the option to start in windows so I assumed something went wrong with the installation. So I then removed the partition via boot camp, however this still left my macbook super slow (at start up, and sometimes RAM usage would be huge for no reason causing lag).

So I decided to erase my macbook drive and reinstall OS X.

This hasn't solved it, and I am still left with my mac saying the physical maximum memory of my HD is ~ 406GB (missing the 90GB).

My model is Early 2015 MacBook Pro.

Please Help!!