If you can't get a word out, pause, find your rhythm and try again. If it's a really tough block, you can substitute a different word. Or just ride it out. It's gonna take a while but you'll find tricks to improve your fluency. But the only way to find what works is to find out what doesn't. You're lucky because you can feel a block coming. Now you can start adjusting on the fly and change your vocabulary to fit your speech. It's a process but you'll get it