See if you can determine exactly where the smell is coming from. I had something that may be similar, and it was coming from under my breasts. It turned out to be a fungal infection - it never hurt or itched, but there was a strange odor.
Getting rid of it was easy. Just buy over-the-counter antifungal cream, the kind sold for athlete's foot. Apply it a few times a day, every day, for about a week. When you shower, make sure to completely towel dry before dressing. Don't let the area stay damp.
Hm I'm not sure what sour baby smells like. Is this your private area/ your vagina you are referring to?