E.F.
The gas drops are worthless (I know people love them, but they are just something for mom to do while the baby works it through his or her system). Try gradually (over the course of several days) switching to another formula. When my son was that age, the only formula he could tolerate was Nestle's Good Start in the green label (with the probiotics). I know lots of people whose kids could only handle the Good Start as well, but for your son it may be Similac, or Earth's Best, or whatever. Just keep looking for a formula that works. The other thing I did that really worked was to STIR the formula-- not shake it. Shaking it put too many airbubbles in.
The Dr. Browns bottles are the best-- stick with them! Good luck!