Tense jaw?

Have you had an uncommon amount of life stress lately?
Maybe you are grinding your teeth at night, which could cause a sore jaw.
Or, have you been having any sinus problems? An impacted sinus cavity can cause jaw pain.

If your doctor doesn't have any ideas, you could see a dentist for an opinion as well.

I think it's unlikely to be a clear and direct result of weight loss alone, especially if you've been losing at a sensibly moderate rate.

A calorie deficit is a stress, sure; and it's cumulative with other stressors that may be in our life, either physical ones or psychological ones. If you have other stressors in your life, it's possible that the deficit helped push stress symptoms over the edge into jaw tension. If so, working on stress management would be a good idea. (Heck, it's always a good idea, to some extent!)

Have you started a new exercise routine alongside weight loss? Sometimes particular exercises can tighten particular muscles and result in something like this. If so, targeted stretching exercises or self-massage may help. (If doing self massage around neck/jaw, be careful about compressing important blood vessels in your neck for more than an instant.)

Along a similar line, how much weight have you lost, or more applicably, how much shape have you changed? I found that when I'd lost a meaningful amount of weight, I sometimes had to adjust my pillow or other aspects of sleeping position, in order to avoid new tensions in my body, because my shape was different enough that my spine was bending or twisting more in the old positions. I don't know whether that's unusual, but it happened for me. (Six weeks seems pretty fast for that much change, but it's possible, I guess.)

Just a couple of extra thoughts for you to consider. Mostly, I agree with those commenting above. I've used a custom (dentist-made) night guard for literally decades now, for similar reasons. Tooth gritting or grinding at night is fairly common, and worth interrupting: It's hard on teeth. I first got my guard after needing a couple of root canals from bearing down for a long time on those teeth!

Best wishes getting to the root cause and solution(s)!

I once had TMJ and it wasn't caused by stress or medication. At the time I was spending my hours at work reading files on my computer screens. I wasn't entering data; I was just reviewing the files. I had a U-shaped work station and while I was working I'd have my right hand on my mouse, rest my left elbow on my desk, and rest my chin on my left hand. The constant pressure on my chin caused the TMJ. Once I stopped that habit, and stopped chewing gum (which I had been doing more than usual to help with my weightloss) the TMJ went away and has never come back.

I'm not suggesting that that is the cause of your jaw problem, but sometimes small, seemingly inconsequential habits that we have can lead to bigger problems. Its never a bad thing to do a self-assessment regarding where your stress levels are sitting, but also review any physicalities that could be contributing to it.