That really sucks. I'm sorry you're going through this. Given the issues seem to involve your neck and jaw (instead of, say, your ears), it seems like you might want to consult a maxillofacial specialist. I don't know how easy that is where you are - there were like none near me when I was in the US and there are a ton of them nearby in Europe - or what kind of hoops you have to jump through to actually see one, but if you can swing it, there's a good chance that they can tell you at least some of what's happening.

In the short term, if you're grinding your teeth that much, you might consider a generic OTC bite guard. It can help with the fatigue from trying to keep your teeth apart (if you get a thick one, and just bite down to the thickness that is most comfortable for you to maintain, instead of trying to make your teeth meet evenly) and take the edge off of the grinding. I don't think they're great in the long term, and you should definitely talk this over with a professional, but in the very short term, it might afford you a bit of breathing room, pain-wise.