I have a female chocolate labrador and she is very greedy so when my dog is sick I assume it's due to overeating! That is what I thought anyway but I don't over feed her and certainly never give her treats at the table. Then I found out that the neighbours son was throwing away his bread rolls into our garden - not great for my dogs health and probably the cause of my sick pet. After getting that sorted out I thought she would stop being sick so often but it still continued. I spoke to the vet about whether I should be getting some dog treatment and explained how my dog is sick and when it happens. She suggested feeding her 3 times a day rather than twice.
This did improve it but when on holiday in the summer it got worse - my dog vomiting at the camp site was not good. Very embarrassing when my dog is sick in the middle of the playing field.
Anyway I found a book about dogs and came across some helpful stuff. Have a look at my post If your dog is sick try this.