Not all applicants can complete the two or three step process as quickly as others. It also may depend not only upon the USCIS, but the consular or embassy where immigrant visa processing takes place and the number of officials available and the number of applicants applying for visas. It may take a year or more in some situations.
If you have concerns, then I recommend an appointment or teleconference with an experienced immigration attorney.
The above is general information and does not create an attorney client relationship.