Jaw locking and limited movement?

For as long as i can remember i cant open my mouth completely without twisting my jaw, if i open it straight it kind of stops halfway and its like one of the bones are sliding against another very harshly. I ignored this but now my jaw keeps kind of locking in a weird position and i cant move it at all. And for some reason i always dream about my jaw locking as well, not just once or twice but extremely frequently even when i havent thought about it and in my dream its quite painful but when i wake up its fine. When this does happen (in real life) i just sort of relax and after a while i can move it again, Its happened quite a few time and is very painful. Also, once when i was younger (around 8-10) i woke up and one of my back teeth were crushed completely and was bleeding a lot that my dentist had to pull it out, but i cant remember the reason. I told my current dentist this and she just gave me some exercises but they arent working. Im only 15 by the way. Sorry if this is so long but i dont know if its all related or what.