See if you can call your lenders and explain your situation. They'll try and help you consolidate your loans, since they want you to make your payments after all, LOL.
It's kind of a catch-22, since you need a good credit score, but the only way to get one is by keeping good credit, which involves having a credit card and rent payments.

I've tried to cancel my old credit card, but the lady on the phone explained to me that even if I don't keep a balance on it, it adds to my score and benefits it. (Since then I've made one late payment oops...but if you keep a really good eye on it, it doesn't make much of a difference.)
The most important thing to do now is to work on improving it. If you've got lousy credit, but if you work really hard at improving it for 6 months, you'd be amazed how much it helps. Call your lenders, make your payments, and stick with it.
My college had a personal finance seminar for seniors,
and they said that to maximize your credit, you should keep a maximum credit card balance of 30% of your limit. (Like, if I have a card with a $10,000 limit, I'll keep an optimal score if I keep the balance at or below $3,000.) It's rather unintuitive, but that's kinda the way it goes. I've gone over it a lot, but it won't kill you. Just something to keep in mind. The most important thing is to make your payments on time.
Good luck!