My english mastiff pup has a bump on her head?

my 4 month old female english mastiff has a bump, I have another mastiff who does not look near as cone headed as she does. I think it is her bone, not a growth, on the middle of the back part of the top of her head. It is very visable although I never even saw it when I got her and seems to become more and more pronounced as she grows. She has also had problems with diarreah that is getting a bit better now that she is eating large breed puppy food. The vet didnt think anthing of the bump. I keep thinking back to a cat I had years ago who developed a very similar lump, but she also had vomiting and weight loss, I took her to the vet and she had liver failure from an unknown desease and I cant recall the exact words of the vet but about the bump, but he said something like it was her bone but I should not be able to see and feel it like that, that it was an effect of her condition and something like, the ligimates or tissue had pulled away from it and that was why it looked that way.