They may have more candidates to interview. The person(s) doing the interviews may have had to set them up so the schedule was staggered according to what was already scheduled. That happened to me once. I interviewed during the first week of the month. The interview went well and she told me she wanted to hire me but that she had one more interview.
I went home confident. FIVE long miserable weeks crawled by. No word at all. Nothing. Zip. Zilch. My mom happened to call just then and when I told her I was still waiting, she suggested I come home for the weekend and go back Monday morning. It was about 150 miles and I went. About 10:00 am Monday morning, my cellphone rang. I got the job!
The reason it took so %$&# long? That final interview had been scheduled for the Friday I had gone home.
Don't give up yet! All sorts of things can delay hearing or checking. One manager told me that if she likes candidate, she may not bother to check references. Don't give up or lose confidence.