Hi Lila.  
 
I also sing in my car, but usually only when I'm in an exceptionally good mood, or when I'm on going on a long trip (it helps to pass the time).  I'm not sure how exactly I sound when I sing, as I always do it when I'm alone, but I do try to sing in a higher rather than a lower pitch.  
As far as whether it feels like something relatively small is killing me like this, I would say yes and no.  Yes, there are aspects of myself I would like to become more feminine.  However, I try not to dwell too much on what can make me feel horrible about myself and that I have no real control over.