I've never experienced stomach pain related to PTSD, but wanted to share with you that from my experience it is entirely possible.
Trauma is stored in the body, and so experiencing physical symptoms is not unusual. For me, I have a spot between my shoulder blades, where when I was doing EMDR for trauma, it felt like I had a rotating ball of knives. It still hurts a lot whenever I'm experiencing trauma symptoms.
I wish I could give you some practical advice on what to do aboto do about it, iut it, if it is trauma related, but I've never found anything that worked for my back, except to ride it out.
Hope your symptoms subside soon.

splitimage