My 6 month old daughter has started a rash on her lower back , we don't think it is a heat rash because it only got worse when she ate her food?

Doctor can examine: Rashes are very hard to describe, so usually have to be examined to tell what they really are. One's primary care doctor can help decide if and when a rash needs to be looked at. If a child is acting totally normal, and only has a faint rash, parents can usually wait a day to see what will happen. If the skin is getting blood spots, forming blisters, breaking open, etc..., an ER doctor can check.