Hi rohitmanglik,
First off, a 690/Q50 is a fantastic score (it's just shy of the 90th percentile overall), so you should apply to any Business Schools that interest you. By extension, a retest is probably not necessary.
The process of applying for accommodations on the GMAT is a bit more 'involved' than most people probably expect (it can sometimes take up to a couple of months just to go through all of the 'steps' and receive the final yes/no result). If you've only recently been diagnosed, then that might also be a factor in whether you receive the accommodation or not - I've only ever heard of (and worked with) Test Takers who had a long, documented history of dealing with ADHD.
So, if you're planning to apply to Business School soon (upcoming Round 2), then you might not have the necessary time to go through the entire process and retest.
1) Do you know which Schools you plan to apply to?
2) Do you know when you plan to apply?
GMAT assassins aren't born, they're made,
Rich