Here's some info I found online:
Puppies and kittens are not infected with coccidia at birth. Normally, a kitten or puppy comes into contact with its mother's feces soon after birth. If the mother has coccidia cysts in her feces, the juvenile animal is likely to ingest them, allowing the coccidia to enter and multiply at a rapid
rate.
Typically, the time period from
exposure to coccidia cysts to the onset of coccidiosis is just 13 days. Therefore, most puppies and kittens with coccidiosis are at least two weeks old. Though most puppies and kittens are infected by their mothers, many
contract the highly
contagious disease from other animals in shelters, animal hospitals, and breeding facilities.
Stress plays an important role in coccidiosis. Often, a puppy or kitten will carry coccidia with no obvious symptoms, only to begin exhibiting signs of the disease when faced with
stressful situations. A change in ownership is an example of the type of stress that may provoke a case of coccidiosis.
Coccidiosis is treatable using
medication. Common medications used to treat the disease include sulfadimethoxine, amprolium, and trimethoprim-sulfadiazine. These drugs do not heal the disease. Instead, they work to impair the ability of coccidia to reproduce, allowing the animal's
immune system to develop and eliminate the protozoans. Typically, medication treatment lasts five days or more.
I don't know your vet, but if it took mine 3 weeks to get back to me with a diagnosis, I would definitely be vet shopping.