I Have Had Diarrhea For 3 Weeks, Am Losing Weight,
Giardia is possible
Detailed Answer:
Hello, I'm Dr. Branch, thanks for using Ask a Doctor. At this point, your diarrhea would be considered persistent, and has lasted longer than expected for most bacterial and viral causes. Therefore, testing for ova and parasites is recommended (including for giardia), as they are more likely with diarrhea lasting this long. If that does not reveal the cause, and the diarrhea continues, endoscopy (colonoscopy) may be needed to look at the colon and take further samples and/or biopsies to help determine what the cause could be.
So I would definitely see your doctor about this so that you can get your stool tested. Your doctor may also want to check your blood to look for any signs of dehydration or infection.
I hope that helps, please let me know if you have any questions about any of that, and I would be glad to discuss it with you further.
Possibly, but unlikely
Detailed Answer:
It is possible to get Giarda from dogs or cats, but it is rare, since the types that usually infect cats and dogs are different than the type that infects humans. But given that your dog likely had it, that could increase the chances a bit.
Normally giardiasis is treated with either tinidazole or metronidazole. I hope you get the results back soon and it clearly shows the cause.