Remove completely all packages I installed?

List all the files in the reverse order of their installation date into a file:

rpm -qa --last >list

You'll get lines like

atop-2.1-1.fc22.x86_64                        Wed Apr 13 07:35:27 2016
telnet-server-0.17-60.fc22.x86_64             Mon Apr 11 20:10:43 2016
mhddfs-0.1.39-3.fc22.x86_64                   Sat Apr  9 21:26:06 2016
libpcap-devel-1.7.3-1.fc22.x86_64             Fri Apr  8 09:40:43 2016

Choose the cutoff date that applies to you and delete all the lines that follow it. Give the remaining lines to yum to remove, after removing the date part. Eg

sudo yum remove $(awk '{print $1}' <list)

You can also try with yum history and usually you get a numbered list of what has been installed, like :

[root@localhost ~]# yum history
Loaded plugins: product-id, refresh-packagekit, subscription-manager
Updating Red Hat repositories.
ID | Login user               | Date and time    | Action(s)      | Altered
 3 | root <root>              | 2011-09-14 14:36 | Install        |    1   
 2 | root <root>              | 2011-09-12 15:48 | I, U           |   80   
 1 | System <unset>           | 2011-09-12 14:57 | Install        | 1025  

and you can use afterwards yum history undo 3 for example.

More details about yum history here.