Tom, Merck suggests that people should discontinue after 1 year of use if there has been no response. I personally feel it should be 2 years, because I have seen people report they saw results during year 1 and year 2.
There isn't any evidence that suggests finasteride can actually speed up your hair loss. You may just unfortunately be going through some aggressive loss. If you had not started on finasteride when you did, chances are you would be in a much worse position now.
If you are tolerating the drug without issues, there is no harm staying on for another 10 months and gauging your results. If you haven't already, take some good pictures of your hair now, and compare (with the same hair length) every 3 months to see what's going on.
You can also consider another 5ARI, dutasteride. It inhibits 95% of DHT versus 65% like finasteride, and is shown to be much more effective than finasteride with basically the same safety profile.
Best luck, hopefully you seen some results soon.