This disorder has been going for a couple of days and your dog seems to be active although he is little by little losing strength. You haven't discovered the cause, yet you must do something. In these cases we refer to it as pertinacious diarrhea, although this is not a diagnosis. A complete fasting period would do your dog good; however, you don't have the courage to impose it on him. So, prepare an oatmeal pap in a medium-sized pot and flavor it with meat extract. In this situation, do not forget to put salt as it is especially important. Offer your dog a small hot portion of this pap four times a day. This can be kept in the fridge for a couple of days. Eve though the dog may not want to eat, you have to insist at least for three days. Soon he will start to sniff theand, eventually, eat it. In the beginning, feed him until he is satisfied, but don't oblige him to overstuff himself.You should also give him lots of liquid, in particular black tea and some water.
Products with spasmolytic and analgesic properties have good effects. You can ask your veterinarian for them; they either come in the form of a pill or a suppository. In extreme case, the doctor may administer an injection.
Suggestion: In case of a diarrhea, try the following diet: salty bread sticks along with a fizzy drink (eg. Kola Real or Pepsi). Mostwill like it, though not all. The effect is convincing in most cases.