I was banded on 4/12 & have experienced those same pains. To be honest, the gas has been the worst part of everything! I don't have the shoulder pain, just the terrible gas & constipation issues. I walk A LOT so that does help, but have also been taking mirlax,milk of magnisum, enimas.
I read that the gas pains can last up to six weeks.... OUCH! Once I get past this issue I will be a very happy girl.