I received a cortisone shot in both shoulders 6 days ago. ever since i have had stomach pains and bloating. are these side effects, and if so, how long will they last?

It could be a coincidence rather than the side effect of intraarticular steroid injection but we can't rule it out completely. Before having the steroid injection I wonder if you have taken any medication for the joint pain which is likely the culprit. If you still take med for joint pain, stop it; if you do not, take antacid (Mylanta or Maalox) for a couple days.