What can I do about my fear of speaking to crowds?

Toastmasters. Try going to Toastmasters, you can go as a free guest and try it out. Challenge yourself to just do it and you will get better. Here is the website for you: https://www.toastmasters.org Good luck.
Desensitization. Work yourself up to it slowly. Look up desensitization for conquering phobias like this. For example, start by speaking to yourself in a mirror. Then to one friend. Then to a small group of friends. Then to a small group of strangers. Then to a larger group of strangers. And so on.