I remember when I was researching the surgery and saw all the references to shoulder pain and thought it curious. Why would the shoulder be affected by a surgery involving the stomach!
From what I've read, the pain is caused by a combination of gas pumped into the body for the surgery and nerve irritation at the diaphram level. Since it's referred pain, icing doesn't really do a thing. I found that walking as much as possible helped a lot. The more I walked, the less pain I had.
You're only 3 weeks out, so it's very likely that a lot of it is still gas pains. Walking will be key.
Patience. It WILL get better. I know how hard it is, though. I remember that the shoulder pain was worse than pain associated with incisions and even the wrap itself. It's very annoying, but it will dissipate and gradually get better. Try the walking...you might find it really helpful.
Words of wisdom by Eckhart Tolle:
"Whatever you fight, you strengthen, and what you resist, persists.”
“Worry pretends to be necessary but serves no useful purpose”
“Accept - then act. Whatever the present moment contains, accept it as if you had chosen it. Always work with it, not against it.”