Conversion rates dropping

I've been promoting a dating offer on FB for the past several weeks. For the first week, my CR was around 15%....a week later, it'd dropped to around 9% and now I am between 4-5%.

My question is - does it have to do with the demographic (I doubt this because the audience is 2mil+)? Am I getting shaved/scrubbed? How can I tell if this is the case? Should I inquire with my AM about the large drop in CR?

CR is the main thing. Always try to keep it in exact level.

If you've been promoting the same offer for weeks without any problems then I'd say it may be unlikely that your leads are being scrubbed by the advertiser. There's a possibility that your leads are being shaved by the network, depending on which network you are using. Have you experimented with Facebook lately? Can you be sure that all fans on Facebook are seeing your posts? Check your edgerank. If you're still having problems, you could always try using a different offer and see what kind of results you're getting from that.