I myself find that the volume you can make with your voice is like a muscle—it is weak at the moment, but when you use it more, it will be stronger and you can speak more loudly in that pitch.
I remember just a year ago when I went to have dinner with a friend, I struggled to keep speaking over the background noise, even though like you I could already speak confidently when doing so softly. But when we had dinner again not long ago, I could talk to her non-stop for 3 hours over the noise without any problem. I think it's because I've kept using my voice the whole time in this one year of time, including talking a lot on Skype to online friends (whom I don't know in real life) and also going full time since half a year ago. So I think if you just keep using it (by that I mean just speaking normally, and not trying to practise speaking loudly—I never tried to practise speaking loudly at all, as it just strains my voice), it will get stronger by itself and you can speak a lot more loudly eventually!
And I don't really know what pitch you use to talk, but I find that my talking voice actually sounds more feminine in the low range, with a baseline pitch of about 160 Hz, so perhaps practising sounding more feminine in a lower range might be a good idea too.