Lump on my duck's back

[Blueberry780]

Blue, my one year old male jumbo pekin duck, has a lump on his back. It's bigger than the size of an egg, and it's causing him discomfort. He is struggling to get up and walk because he is doing a gagging motion. He is also nibbling on the lump. I checked under his feathers and i don't see anything external. I notice that the lump appears after he eats, maybe about 30 minutes later. I gave him some water, and massaged the lump, and the lump went down in size and he stopped gagging. The lump felt hard, like a cramped muscle? I just don't know if he had food stuck there but I don't think food would travel down his back... Also his neck is moving very weird, he's bending it so he looks like he has a rectangle head, like he has a forward head if that makes sense. When I touch his neck one bone feels off it just don't feel right. I don't think it's broken, I just don't know what it is if he has something stuck. Just to mention he has a slipped hock joint, so he already has trouble walking, but I carry him everywhere and I make sure his space is limited and he is close to food and water. I don't know if the lump could be connected to this. Also, since he is male he has a curled tail normally but I know they go through molt and they get a new one but blue has not gotten the curl back its been 2 weeks and no curl. His quack is still raspy though. Again idk if this is connected to the lump.
vet is not an option

(He is in a bucket because I bring my ducks inside at night since we are still reinforcing the coop)