ummm this thread is so big, it takes forever to search it, so sorry if this is here already by someone else...I've defeated the elite four and found strength, but how do you get to pacifidlog, anyways?
I assume you didn't go to Lilycove Sewers. Fly back to the E4 and walk south until you get a phone call. Then you can go to Lilycove Sewers and progress the story (after getting through you will automatically go to Pacifidlog).