Summer - Great job on paying down the debt!
What probably happened is that you were in the "bucket" of people who have say $5,000 of debt. You were rated at the top of those people because you were paying down the debt, paying on time, etc. You paid off the card and you "graduated" to the next bucket. Now you start at the bottom of those people because some of them have longer credit histories. Hang in there, it will get better! And I agree, do not close any accounts.