After breastfeeding exclusively for the first two months, I too ran into the same nighttime gas issue after a month or so of introducing the similac advance formula. When gas drops really didn't work, I switched him to soy. Almost immediately I noticed a huge difference. We did that for about 4-5 months. In that last 2 months switched him over to similac sensitive (milk based but lactose free) which has worked well too. I am hoping that slowly re-introducing regular stuff as he gets older and his system matures will work so that he is not lactose intolerant.
I never even asked my doctor to change formulas, I had mentioned several times that we were having serious issues at night and really got no great response from her, so I did it on my own. Only when we went to his 6 month appt did I mention that I had switched him to soy with success and got a "oh good, that's great".