Usually if its getting ready to lay an egg, the area in front of the vent will start looking enlarged. From your description of the location, my first thought was possibly a lipoma or fatty tumor. They can also get cancerous tumors too. You need to get him vetted and have a blood chemistry done to make sure his liver is okay too if it is indeed a lipoma. And possibly surgery to have the tumor removed. Those things will continue to grow until they ulcerate causing all sorts of misery and can in the end become life threatening. If it is fatty, then his diet will likely need an overhaul too. You'll have to consult your vet about that. There isn't anyway out of this, you've got to see an avian vet unless she pops out an egg in the next few days. My females don't normally have much of an obvious lump though for an egg.
