What can cause severe abdominal swelling in a dog?

My 7 yr old Jack Russell Terrier is bloated. He was seen by vet but no blood work or XRays taken. Vet said it
could be Congested Heart Failure. He put dog on Lasix 3 days ago and said to watch him! I’m watching him get bigger and bigger…. he’s peeing and peeing and drinking lots of water but won’t eat food, can’t poop… just turns circles when attempting a BM. He scoots his butt on the ground and gets more anxious because nothing will come out. I am willing to try anything safe and natural to help him. Got any suggestions?