My regular physician had me on finasteride about 6 months before I began standard cross-gender hormone replacement therapy that knocked my free testosterone near to zero and gave me high levels of E. My libido and responses are very different than they were in boy mode, but not less. One of my pet theories is that brain and sexual responses to medications depends in part on the unique configuration of our brains. I can only speak for mine, that I prefer the multiple, full body orgasms that I routinely experience now to the localized wham-bam-thankyou maam o's that I usually had in boy mode. It takes me more to get interested and revved up than it did when my brain was in boy mode, but when I do this motor can really roar, for hours and hours.
Finasteride probably has a more profound effect on a brain that is already configured for a female pattern-- its going to take more than reducing DHT levels to knock down most men's libidos. I would just advise you to 1) get totally checked out to rule out all the scarier-than-a-reaction-to-fin possible reasons for your symptoms, and at the same time 2) don't worry about your sexual response being permanently gone. It comes from the brain, and it adapts to all kinds of life changes minor and major. It can be disconcerting when there are changes, but in the absence of serious untreated medical illness, it comes back. Oh yes. And not only can you get off by prostate stim, but also by a lick, a kiss, a touch, or the thought of a gentle breath on the back of your neck... whatever pushes you over the edge while feeling safe, loved, and wanted for who you are.