I know it's crazy....You're not alone in your frustration. The reality is that Fannie Mae agents and the asett managers they take direction from are all heavily loaded with files. Communication and timeliness go out the window with the current workload. You agent should be constantly reaching out for an answer (the squeaky wheel does get the grease), but don't expect to get the deal if you're not the highest and best offer. You'll find this is not just Fannie Mae, but almost all REO sellers.
In my market area, we routinely see REO sellers wait for a multiple offer situation (preferably with a cash buyer) prior to responding. Last night, I just got news that the seller, after issuing a multiple offer addendum and requesting a highest and best by a deadline, balked and didn't execute any offer! I understand the strategy, and of course the seller has no obligation to sell, but I will be watching that seller in the future. It's real estate, not used cars people...
My advice to you is to request that your agent routinely check in for an answer, and that you be patient with the process. Make sure your offers are well thought out and that you are studying the comparable sales, especially Fannie Mae sales, in the area. This way, your offer is commensurate with other similar REO sales and you're more likely to get a positive response and be more competitive in a multi offer situation. Also, take advantage of the First Look program. This is typically the first 14 days of the listing period at which time the seller is not considering investor offers. This practically eliminates cash deals and gives owner occupants a strong advantage. An REO seller's participation in First Look is done to show a commitment to Neighborhood Stabilization. Since all these banks are floating on federal dollars (our taxes), they have to take owner occupancy very seriously for political reasons.