I can’t open my mouth that wide and I have lockjaw I don’t know what I should do 😩

So when I open my mouth I can hardly open it that much, my jaw feels heavy and just wont let itself open wide, then my jaw also shifts when I sneeze or eat & it feels like I get lockjaw

My dentist did say I need to get braces for these reasons cause I also have a slight overbite but my question is how long can I wait to get braces? Will these problems get worse? Do I have to get braces urgently?