I have a 3.5 month old that has this big hump looking thing growing under his neck. I have no idea what it might be but it keep getting bigger and it's hard. It doesn't seem to have pus or any spots so far but it is a tough to touch ball like growing under his skin and is getting hard for him to walk. I know it's not much to work with but I hope someone knows what I'm talking about and can help. TIA!