Try practicing speaking from your diaphragm - make sure your voice is resonating from in your upper chest as you speak, rather than the back of your throat, or pinging around inside your sinuses. It helps to keep your back fairly straight, so you can get a full breath.
If you learn to speak clearly this way, your voice will "carry" better, without you having to "raise" it until you feel like you're yelling or talking too loud. You will have to practice it while you're alone, until it becomes second nature, then you won't even realize you're doing it.
It's a technique professional singers and broadcasters have been using for years.