Some people wait several years before getting their permanent residency after the interview. Some people get the physical green cards with a few weeks.
Without knowing more facts about your case, no one can opine as to how much longer your case may take.
Even knowing many details about your case, sometimes it is difficult to guess how long the processing takes. Processing by USCIS sometimes is inexplicable.
Did the interviewer ask you to submit more information? If yes, have your complied?
Did the interviewer give you any indication as to what the decision may be?
You can contact the national customer center or schedule an InfoPass appointment for follow up.