I knew a couple a people who had rsd in the stomach. One girl specifically she would become dehydrated because she was unable to keep fluids and food in her system. Her limbs had rsd as well. After many failed treatments she found a treatment that helped her overall with her rsd so now her stomach is doing much better along with her limbs.
As for constipation I think between meds,lack of activity,stress etc for some it can cause consitipation. I have such a sensitive stomach. Spicy foods and me don't mix at all.
I hope you feel better.