Johanne

For many of us here, 38mm would be wonderful. The standard test for trismus is whether you can stick the middle three fingers of your hand into your open mouth. I can't help you with stretching advice as after three years of daily jaw stretches, I'm only back to 28mm. It doesn't impact me much though due to my feeding tube.

Now the obturator headaches is another matter. I'm on my second one and my experience was that improper fitting was the cause of my headaches. Not sure how yours is held in place but mine has a wire hook on each side that snaps into grooves /channels drilled into the biting surfaces of my teeth. My prosthodontist had to adjust each of mine several times before getting it just right. I'm not talking big adjustments, just a twist of the wires or a dab of that fitting goo over top of a slight dip in the molded surface.
The point is that it should not hurt nor cause a headache and if it does, then it's a fitting issue. Just like you can make yourself "get used" to ill fitting shoes, but you end up with blisters, an ill fitting obturator doesn't resolve itself in my experience. My prostohdontist gladly saw me multiple times without extra charge to get my fittings right. He did ask me to wait a week but felt that if it didn't feel right by then, it wasn't ever going to without an adjustment
Charm