Getting guild rep!

Hi guys!
I have a slight problem with my guild reputation. I am at 13000/21000 reverd but i dont no where i can get more rep points so i came here to see if you could help me. Btw i want to get exalted to get the mount :)
Hope you guys can help me!! Sargeras, Allstayer, DK Blood Human!

Theres a cap on the amount of guild rep you can get in a week, just wait for it to reset.