Is soymilk good when you are trying to conceive?

Soymilk for concepti. No, some studies have pointed in other direction that soybean and soy foods can inhibit fertility, only if consumed in large amounts. So to improve your chances for coception, avoid soy products.
It's OK. Soy milk can be part of a healthy diet especially if you are allergic to regular milk. A low glycemic index diet is a healthy one and is associated with higher fertility rates. Take a look at the fertility diet, a book by dr chavarro and his harvard colleagues for some specific recommendations backed by scientific research.