Evelyn : That, too, takes practice, I think. For me personally, it felt like literally training my voice - like the more work I did with it, the stronger it got. I had training as an actor in projecting, though, so that probably helped. I can now even scream instructions in a higher pitch, although it isn't particularly my "best voice." (I'm also lucky enough that my natural vocal range is from mid-tenor to low alto, so I'm basically striving to hold "head voice" and end up in a feminine pitch.) I didn't really get good at speaking loudly until I was doing the female voice 24/7 for like a year.
And yes, even so, I don't have quite the projection or power I did before. Oh well.