I'm not sure if the pork skins is a part of the problem but it is an interesting thought. I know someone who's 3 year old French Bulldog throws up white foam anytime he eats a pork skin product. I would definitely suggest that both the OP and angelkiss bring their dogs into the vet ASAP. If it is something more serious like parvo then time is of the essence. I would suggest possibly asking your vet about any connection between pig skin and vomiting while you are there.