Dogs don’t make themselves throw up in order to get it to eat it again. Throwing up for extended period of time, particularly after a meal is a concern.
If stomach content comes out “on its own” without any heaving, it’s called regurgitation. That can have its own set of causes, such as megaesophagus, which is pretty serious stuff. Is he losing any weight? Reasons for vomiting can range from issues in the digestive system itself to systemic problems such as kidneys or liver.
With your set of symptoms, please do take him to a vet and have this diagnosed so you can treat it accordingly.
http://dawgbusiness.blogspot.ca/2015/01/symptoms-to-watch-for-in-your-dog.html
http://dawgbusiness.blogspot.ca/2015/02/symptoms-to-watch-for-in-your-dog.html
first: i’m very, very sorry for your loss.
second: a necropsy is the best way to determine this at this point. i would consider it.