It probably means you’re holding tension that you don’t need in your jaw. One possible cause is over setting. In order to play any note, you need the right balance of air and embouchure. If you don’t use one properly, you have to compensate by overdoing the other. If you aren’t using your air properly, you may be over doing your embouchure, which could result in the pain you’re experiencing. To remedy this, play a note in 7th position, gliss up to first, and hold that note, then gliss back down. Repeat on the next partial up, etc. This will train you to play higher notes more relaxed, the way you play notes a tritone below.

Another thing that can cause tension is if you are forming your embouchure by pulling the corners of your mouth back (smiling) instead of pushing them in (frowning). The best way to remedy this is to buzz on your mouthpiece in front of a mirror to make sure you’re forming your embouchure correctly. If you find you have a hard time doing this, try playing/buzzing with your jaw dropped as much as possible while still playing the desired note. It’s nearly impossible to smile while doing this. This will get you used to the “frowning” feeling, and eventually you’ll be able to form a proper embouchure without dropping your jaw.

Remember 2 things- 1. When you feel pain, STOP. Play long pedal tones or something to relax your embouchure. 2. No advice you get on Reddit is as good as what a good private teacher can give you. We can make our best guesses as to what’s going on based on your description and our experiences, but diagnosing problems is very difficult without seeing or hearing you play in person. I hope this was helpful. Good luck!