Why do I always run out of breath??

I’m by no means a fan of public speaking but may have to do it at times for work. I’ve found that whenever I am giving a presentation, I tend to run out of breath or catch myself holding my breath and my voice gets shaky and I know others can hear it. I assume this is due to nerves and anxiety but how can I fix this or work towards a solution? I try to catch myself before it happens but often times it’s too late and I’ve already ran out of breath so now I have to slowly exhale during pauses without making it obvious but I know my voice quivers. Any advice would be appreciate!