Experienced Odeskers, How much money do you make every month?

I started working on Odesk last October. I have completed over 130 projects so far and have gained a rate of 4.98, and have made about $9,000 in the past year. But the problem is that I am getting fewer and fewer projects in the recent 2 or 3 months. In the last 6 months, I made about $3,900; in the last 3 months, I made about $1,700 and last month I made about $500. It is getting harder and harder for me to get new projects from new clients. All my recent projects were awarded by my previous clients. I do not understand why this happens, since I have good feedback; I work hard; my rate is reasonable. I create each cover letter very carefully. I just don't understand why new clients don't want to hire me. Are there any experienced Odeskers who have the same problem? Am I the only one who suffers from this? What should I do?