immigration interview.

I got interviewed 2 weeks ago in LA immigration office.
My wife is a American Citizen. Immigration officer told us every thing is ok,but he cannot stamp I-551 on my passport on the same day of the interview.We just need to wait for the background check for 6 weeks, then they will mail me a letter. 6 weeks?! Please tell me something about the procedure, and how long?.

The officer also said I cannot walk in to check my status until 6 month after my interview, and they won't appove my AP application because my case is pending, I shouldn't go abroad.

Any peice of info is appreciated.