Are you on the electoral roll where you are living now? Is this address one that you'd consider 'permanent' ie as opposed to just sleeping on a mates sofa sort of arrangement?
If you're not on the electoral roll, get on it and that should sort out your credit agency issues.
However, I wouldn't use Experian as they charge for their services and not all lenders use them. You want the Money Saving expert credit club, or credit karma, both of which are free.
I also don't know if your credit file will include all your debts if they're registered at another address but it's a start.
The information posted by @autumntimebrowns looks useful in tracking down debts you've lost track of.
But it does sound like a DRO might be your best bet, providing you have no assets and no disposable income.
So the other thing you can do to help yourself while you're trying to identify your debts is to draw up a sustainable budget without any debt repayments. You'll also need to do this to get any formal debt help, so it's good to make a start.
Make sure you include an appropriate amount for food, travel, toiletries etc and even emergencies as you need to cover everything you may need without borrowing as you'll be effectively banned from credit for 6 years.
When many people start to slide into unmanageable debt, they often make the mistake of cutting back on food or other essentials in order to pay their debts, which is the wrong way round. Obviously you shouldn't be living a life of luxury while you're trying to get out of debt, but you're not expected to sit in a cold dark house eating cold beans either.
Have a look at www.moneysavingexpert.com/budgeting-debt-help/
Good luck 
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