What an interesting mystery!
I have a few friends who cannot wear watches. Digital or analog, they stop working within a day or so. For them I think what's going on is that they are untrained energy workers. They have the energy but haven't learned how to focus.
Breaking a necklace has only happened to me once. It was a strand of garnets connected by metal loops. I was leaning over a sink and it just popped and the necklace slithered down the drain! First thought was the garnets weren't the right stone for me. Second was I was feeling angry and very ungrounded.
So, that's the direction I'd go, to look at how grounded you are when it happens. With PTSD you have a lot of free-flowing energy. I would also vote for @jamethiel's suggestion of an open spiral. Maybe a memory wire type of necklace or bracelet?
I have broken so many watches. XD I gave up wearing one years ago.
I have often referred to myself as like George Clooney's character in The Men Who Stare At Goats in the scene where he walks by a bank of computers and they just all fry. Yep ...that's my energy. LOL
I have some reiki training, but I definitely still feel like even though I can do that, and people say they feel the effects a lot, I am mostly not focusing it and I have a lot of basically sporatic, frenetic, pent up energy.
I also, given the throat chakra busting out all over, feel like that's part of the reason my teeth break. I had a dream either last night or the night before that my teeth all healed and grew back! I didn't remember until just now! I woke up and felt them with my tongue and was disoriented for a minute.
That is a very good dream! I don't 'do' dreams but even I can tell it was a message of healing!
Well then, If I were working with you on your energy the first step would be getting you really grounded. Practice that for a while, then practice throwing out your energy and containing it, feeling the difference. It's like opening and closing your fist.
Energy flows like water. An ocean, a river, a garden hose, depends on what you want to use it for.