What do you do if you can't get a word out

What do you do if you can't get a word out I have a strong stutter but inconsistent. I have good days and bad days. And when I speak I have two kinds of stutters. One where I repeat a certain letter ( like a a a alex) and it usually doesn't bother me much. What bothers me the most is when I can't say the word, I open my mouth and nothing comes out ( I get away with saying "ummm" sometimes but it rarley works. Any advice?