bad diarrhea

My dog is a 10 years old Golden Retriever, he started a non stop diarrhea 3 times a day (yellow watery ) for 30 days and can’t seem to stop. He’s not eating well and is lethargic. We took him to the vet but treatments are not working either and there’s nothing wrong in blood or fecal works...

Poor Biscuit has been up every 3 hours during the night with explosive diarrhea. He's gone at least 7 times. The first time, I thought it was because he hadn't eaten enough (he often has diarrhea when he's hungry, but not explosive diarrhea). The second time, he begged to go out. I was super...