Just keep checking back with your agent (or the listing agent if you are working with them directly) every few days. I would recommend that contact be by email as much as possible. As an REO listing agent - I'm usually buried in paperwork or on calls with my asset managers and banks. I can shoot off a quick response to an email while I'm on the phone or in the middle of something so you'll get an update a little faster.
Best of luck on getting a favorable response to your offer!
Kelly Gebler, Principal Broker
Keller Williams Realty
After the bank accepts, they forward their addendums to the buyer. Some agents wait until the addendums are signed before they mark it pending.
Keep looking. There will be others :)