My 6 month old has developed a lump on her neck. I've noticed about a week ago. It started off small and on the left side of her neck, now it has gotten bigger and now moved to the right side of her neck close to her head. it has a soft spot to it but hard mainly. The skin on it is yellow in one spot then a grayish color to the rest of it. It's about quarter size. It's not painfully unless it gets squeezed. She still eats and drinks and free ranges. Does not seem like it bothers her. Can anybody help me figure this out?