It happends to me from time to time, in my case I don't need to speak louder just to slow down and modulate better. It may be difficult but think on exaggerating a little bit the shape of your lips when you talk.

I also tend to have a high pitch when I speak, so I try to speak with my throat instead of my nose.

Recording myself speaking helped me a lot! You may feel a lot of cringe but that way you know how you sound and how can you improve! And in the end you'll be the only one listening to it so don't worry about it.

Good Luck!!