Be patient and realize that the entire process is taking between 4-8 months. There seems to be more posters these days who are worrying although they only applied 2-4 months ago. Stop worrying , you'll get your interview soon.
Bobsmyth, thanks a bunch.... I know I am a worry freak...I started freaking out when I saw applicants of my DO, who applied after me getting their interview letter.
I think you right, I need to be patient.