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I have nearly identical symptoms, and also began taking Propecia in my mid-20s. After taking it a couple years, the side effects became really noticeable. I've been off for 2.5 years now, but no improvement. It's devastating.
The side effects I am experiencing from using propecia are virtually identical to yours. I stopped using it 14 months ago, but I still have severe issues with libido and erection quality.
Generally it takes awhile to get your system back to normal after stopping a medication, however if it continues to be a problem after a couple months, I would have it checked.