Interview Dilemmas

I am an RN who graduated with a BSN Degree in May 2009. I have been applying for RN Positions since January of 2009. I lost my job in November of 2009 and have been looking for positions ever since. I have been getting interviews but it is usually two a month and then a couple of months without an interview. I have been applying for Medical Assistant positions too in the hope that maybe once the market improves I can make a leap while at least practicing in healthcare. The last position I interviewed for was a Dermatology RN position. The advertisement said that they where willing to train and I was really interested in the position. I interviewed a week after applying and I thought it went well. Before I left the interview they said that they would let me know by the end of the following week. I sent a Thank you letter and waited. By the time Friday came around I was on pins and needles... so I called the office and asked to speak to the interviewer who was out of the office. I left my name and number hoping to get a response. It is now Tuesday and I am beginning to feel like I did not get the position. This is not the first time that I have not heard back from an interview but I am beginning to feel like I am doing something wrong. At the very least, I believe potential employers should let interviewees know their decision one way or another. What should I do next??