For gas pains, we always used Mylecon. Wal-Mart makes a generic version of it, and the drug is called Simethicone. It's a harmless drug, as it is not absorbed into the body, but passes right through.
What it does is takes all of the little gas bubbles that are hard to expel, and forms them into a big gas bubble, making it much easier to pass.
I would try that first before switching formulas. You can either put it directly into their mouth, or in their bottle (we always put right into their bottle!)
It works WONDERS!

There are many posts on here about gas pains and using simethicone.
Good luck!