I had heavy heavy platinum highlights for years. I went brunette back in November in an attempt to let my hair get healthy before I highlighted it again. (It was horribly damaged - I cut off several inches to try to get it better.)
Now, the color has faded and is rather "blah" and Im so ready for my hair to be blonde again.
Ive been taking hair vitamins and vitamin e everday to help the condition of my hair. And Ive limited my shampooing to twice a week, and stopped using heat on it. Would it be okay to highlight it, or should I wait?

They recommend after 6 weeks

I would wait a little longer and try to let some of they color grow out because brown is hard to take out sounds like you need a conditioning treatment to help get your hair in better shape putting highlights in we only harm it know be you will be using bad chemicals, so if I were you I would wait, if you decide not to wait make sure you go to a very good hair salon not just any little one maybe get some referrals because when you try to take color out of hair it will only damage it more so you need someone who really know what they are doing so they can give you the right conditioning treatment after oder wise you are going to wish you never did it take from me I tried the same thing and it got so bad that know I am back to dark brown it look great know because of the treatments I had done.