I can't speak?

Hey all, I don't ever make reddit posts so mind my reddit etiquette lol.

Recently ive noticed i cant speak? Like for example during tuition or something else I know EXACTLY what I want to say yet my mouth just can't say it. Like rn as I'm writing this I want to ask my mum "should I go to the doctors to get the registration forms" I'm sitting here opposite from her and I genuinely cannot form the "sh" sound in should. Like 95% of my speaking is fine it's just certain sounds in which my mouth just cannot say. It's not exactly the same sounds every single day, every other day I can say "should" perfectly fine it's just today I can't. Other days is other words/sounds and it's really really frustrating and I literslly have no idea what's happening to me.

On another note I have to change the way or the structure I make my sentences because I KNOW what word I'm gonna get stuck on. This also happens with reading and my tutor gets frustrated with me cause of this. Just for example if I wanted to say "the cat sat in a hat" it would go something like "the.... cat sat in.......................................... a hat"

I KNOW what to say but i just can't get my mouth to reciprocate. Anyone know why this is?