Credit scores are a joke. Mine used to be 720 at one time and always hung around the 700 mark. I now sit at 583 and nothing has changed in my situation...
If your credit score dropped that precipitously in a short period of time with virtually no rational explanation, then you need to inspect your credit report and inspect it carefully.
You could very well be a victim of some type of scam, identity theft, or simply a vendor/creditor/collector continually requesting and/or viewing your credit report.
You can start here --> https://www.annualcreditreport.com/index.action