My jaw is stuck and I cant open it past a certain pointt what do I do?

I havent been able to open my mouth past a certain point since 9:45 this morning, and it hurts when I try to open itt, what do I doo? and Why is it doing thiss? Its makin me scaredd. Also, before I couldnt open it like everyonce and a while it like popedd, cuz I couldnt open it then it poped then it would open but when I closed it again I had to pop it againn, but its NOT popin or goin back to norm. will it eventually should I just let it go? It hurts when I open my mouth to eat 2.. Idk what I should do! Does anyone know how to fix it?? I also have a headachh, Idt that could be anything to do with it but ohh well..... I am a cheerleader and I have to yell with my mouth open,,, and its right near comp.. I NEED It to get better thankss for people that have help :)