Lola, I was in exactly the same situation you were in -- in my case, going to a debt management agency was the BIGGEST mistake I EVER made.
When I went through debt management, my bills were current, I just owed a lot of money at high interest. Anyway, this place basically paid my bills sooooo slowly that my credit ended up littered with 30 and 60 day late payments. And even though I tried to explain this, my creditors refused to make adjustments on my report.
Long story short if you are not working with consumer credit counseling then don't do a debt management plan.
The only real "fix" is to pay everything on time all the time. If you are short, then hold off on the cable bill or the cell phone bill (assuming you have those) -- NOT your credit cards.
The longer it has been since you have made a late payment, the better. And if you can make two years without late payments, your score will jump substantially.
In my case, I'm starting school first and applying for private money in September. By then, it will be two years since the "situation" and my score should be really high.