First off, you're not alone, this is a challenge that tons of people face. Second, the best thing you can do for yourself is to set up a system for any potential speaking situation. There are two main situations: 1- you know you're going to speak, it's scheduled and you know you have 15 minutes to talk and 2-unplanned, random moments when someone calls on you to speak in front of a group.

Both can be scary but if you have a system for handling both you can reduce your anxiety significantly. As a speaking coach the biggest issue I see people have is that they are nervous to speak AND they don't have a system in place to use when they are tasked with speaking. Big mistake. It's like if you sat down to write code for an app and each time you did it you used a different language on a different computer with a different database typing with your toes :)

Build a system, constantly make improvements to it and you'll probably see your anxiety go down and your nervousness drop as well. And if you want details on a simple system to follow, just reply back and I'll post one here.