I agree with the other parents about the specialty formulas. They worked for my friends with the lactose issue. However, has your doctor diagnosed your child with lactose intolerance? If you haven't recieved a formal diagnosis, seek one out.
Lactose intolerance is defined as the inability to digest lactose (duh) and signifies a lack of the enzyme lactase. Lactose intolerance is very rare in babies because they are born with the enzyme lactase (they need it to digest human breastmilk). Lactase will continue to be produced by the body unless one stops comsuming milk or products with lactose. So if you go a couple years without dairy you can develop lactose intolerance as an adult. You can also be genetically predisposed to it.
That being said, I do have some friends whose children have had a milk ALLERGY, which is different than lactose intolerance. My girlfriend's daughter could not even tolerate breastmilk. They have used the allimentum or other perscription formaulas.
In regard to soy. Soy has been touted as a super food or the end to global hunger by many industry leader in the US. However I have some serious concerns about the safety of soy. I have removed most of it from my family's diet except for fermented sources like soy sauce which are more traditional and safer. The below website has some good info for looking at the pros and cons of soy. Not to mention that more than 80% of the US soy supply is genetically modified. I believe GMO products to be unsafe, and if your formula is not organic it is likely that you have GMO soy in there. And there are alot of products that come from soy: soybean oil, textured vegetable protein, soy isoflavones. Many many many processed foods contain a soy derivitive, even ones you might not expect.
But don't take my word for it....Do your own research. Google search it further if this is new info to you.
http://www.savvyvegetarian.com/articles/soy-truth.php