Jaw tightness, but not diagnosed as tmj. what else could it be?

Need more info: For tightness, are you referring to restriction of opening, soreness of muscles, limitation of moving side to side, or something else? Often these are related to clenching and grinding teeth, but there is not enough information to give a more complete answer.

Many things: Could be any of a number of things that restrict oral opening. See an oral surgeon for expert advice.