My dogg is 5 months old a female dogg three days she haven't ate she vomits white foam and is losing weight

You need to get her to the vet ASAP, it could be parvo, a serious and deadly disease.
It could be something else entirely, in any event if she is throwing up and not eating she won't last long.
I would start looking for an emergency vet, In the meantime you can try to keep her hydrated somewhat with pedialyte.
Best to get her in today if you can, tomorrow may be too late.