somethings definitely not right. should be some kind of blockage. i know bloat can be caused by physical blockage, or due to bacterial infection, but i've only seen bloat occuring in the stomach/belly area.
if its gravel, i'm really not sure what can be done. maybe you can try to physically push it out...don't know if thats gonna do anything.
if its not gravel and some other internal problems, you can try adding epsom salt. personally i've used this a few times, but can't say i have success with it.