Hi Josie,
My sex drive went to zero within a couple of weeks of starting HRT. In my case, my pre-HRT testosterone levels were low to begin with, and then got very low on spironolactone. I think this is pretty normal if you are on anti-androgens. My sex drive has never recovered, though, and it has been ten months. Fortunately, I really don't miss it. It just makes things easier during transition, in my opinion.
I should point out that my estradiol levels have barely been above the male range the whole time, so I have been an endocrinological eunuch. Many trans girls report that their libidos return once their estrogen levels are high enough. I have since changed endocrinologists, and I now have a more aggressive hormone regimen, so it will be interesting to see if it makes a difference.
With kindness,
Terri