It sounds like you are doing a Short Sale. If you can be more specific with what has occurred so far, I would be glad to offer you my professional opinion. Is it that your lawyer is negotiating with your lender and is awaiting a response? If so, that can definitely take several months.
With regard to the "buyer's preapproved loan" what do you mean by that? Did your own lender offer some type of buyer incentive?
Thanks for any further details you wish to provide!