Oh man, that sounds really awful. I'm so sorry you're going through that. Is your belly huge just from the intestinal issues? I ask only because that can be a sign of liver issues too, and opiates are hard on the liver. If you've had a doctor check you out recently, I'm sure you're fine. Oxy always knocked the hell out of my appetite, to the point where I lost like 20 pounds and looked like total shit, but I've heard it can do the opposite as well. I did have some luck taking Miralax every day with tons of water as a maintenance technique. Colace too is supposed to be good for opiate-induced constipation. But I'm not a doctor. I'm just speaking from what my doctors have told me.
I asked my ER doctor about the medications they're always advertising for opiate constipation. I saw ads for it all the time online back then. He told me those meds ran at like $500/month. Brah, given the reason I'm here, if I find an extra $500/month, I can guarantee you it's going into my arm and not my colon. Come on now.
I'm not sure about sticking h in your shoulder. Is there a vein there, or are you talking about intramuscular? That one vein that runs between the elbow and the upper shoulder is safe, in my experience. Kind of near where the bicep is. I've always heard not to go above the shoulder, but that below the shoulder is cool. I fucking hate running out of veins. I destroyed mine with my last run. All my faves are still collapsed.