Why is my wisdom tooth hurting so bad? its swelling and i cant hardly open my jaw. and its hard to eat food. and swallow?

Cavity is my first guess without looking and feeling in mouth.

Your tooth is possibly trying to erupt and can't for a number of reasons. Not enough room, causing pain and swelling, food is trapped under gum, causing decay and an infection. A condition called pericoronitis from a wisdom tooth can cause trismus, which is why you can't open your mouth. Now that you know why, see your dentist for exam and treatment and a possible extraction by an oral surgeon.