I'm sorry you haven't received any responses as of yet. Most people on this forum breastfeed and some are anti formula (to put it mildly.) I actually had to use a bit of formula in the begining (my son is over 6 months now) as he never took to the breast (I pump and provide breastmilk in a bottle - too long of a story). I too used Similac though he didn't seem to be affected with constipation or gas. I think it would definately worth a try to switch considering how much pain he seems to be in right now. I'm not sure how old he is but if he is on solids, you could try prunes if they have them there or prune juice. Also, you could try infant message (you may want to google it -- there is a belly message that could help) or bring his legs up to his belly and roll them around or pump them up and down to help move the gas. Sorry your babe is in pain and best wishes!