Hello!
To make it short, your system needs to become multi-user instead of the single-user that it is now. As you said, the registration part should be already working, the interface and everything else is set up, and your system needs the separation of account information so that everyone can only see and access the pieces of information they created, nothing more. If you happen to know, was your system built on some framework? I mean php framework, not the jquery, which is the interface part ? I'm available to start working right away, project will be completed in the 15 estimated days (though I think it'll be less, possibly 10 days). Milestones and payments will be done on 3-4 stages, upon completing parts of the work, as agreed by both of us. No upfront payment required, but a milestone of about 25% of the amount (that's an escrow, I don't ask any release until showing functional things).
Regards,
Dragos