My dog was perfectly fine two days ago but yesterday and today he did not want to eat, so I left to school this morning and came back and he was dead and bleeding a lot from his butt :( does anyone know what caused it?

I am so sorry to hear about your poor dog; I can understand how upset you must be.

The only way to know the cause of death for certain is for the vet to perform a Necropsy, which is similar to an autopsy in humans.

However, there are several reasons why your dog may have died. I don't know if he was vaccinated or not, but he may have contracted Parvo. This is a very serious condition in dogs that will certainly lead to death if not treated immediately.

Loss of appetite is one of the main symptoms along with lethargy (did your dog seem tired and not want to do anything?) vomiting and foul smelling diarrhoea. You say that he was bleeding from his butt, did you notice any diarrhoea at all?

Another thought is that he could have had colon cancer which causes a huge mass to form in a blood vessel. When that eventually bursts, the bleeding will be too severe to be stopped, and the dog will go into shock and pass away.

I know it is hard not knowing what caused his death, and I am sure you want to make sure that you recognise the symptoms and can prevent this in any other dog you may own in the future. Therefore talking to a vet and maybe allowing him to perform a necropsy may be the best way forward.