My name is john. I have a three year old bitch named D.O.G ( dee-oh-gee). Since I can remember, she has had diahrea. Iwould like to learn more about the types of diseases that could cause this

Has she been to the vet? You need to find out if its a bacteria/feeding/worms or other problem first before we can help really. Take her along to the vet asap and let the board know how you get on. You could take a fresh stool sample for the vet to test.

It could be worms, it could be colitis, it could be a food intolerance....

Visit the vet and get her checked out. She should not have diarrhoea for years!