If you "can't see if finasteride is making a difference", then it probably is. finasteride doesn't always regrow a crapload of hair, it will usually just halt the hairloss where it is. So, if you haven't experienced further shedding, then I would wager that the finasteride is in fact working.
Don't make the mistake that others have made..."I can't tell if it's working, so I'll stop" then 3 months later they lose 1/3rd of their density.
Keep it up!